Well, you are certainly in a pickle in this one. Only a Napoleon would seek out such a situation. You have placed your forces right in between two armies. Can you emulate Napoleon?
Let's analyze the starting situation. You have 7 villagers and 17 troops. Hannibal has 7 villagers. Hasdrubal has 10 villagers and therefore ... drum roll ... 24 troops. This is all available from the Achievements menu. You need one House just to catch up to your existing population. You will lose a bunch of units very soon, so you won't need a second House yet. You need a Scout right away, so that you will have better situational awareness. You will want to get a couple of replacement Axemen right away, and now your food and wood stockpiles are all used up, so you cannot afford to get more villagers yet. You probably should build one or two Towers right away. Remember, the Romans get super-cheap Towers! Put two villagers on wood, one on stone (for repairs, at least), three on food, and one can build things. Of course, by the time you actually get around to issuing these orders, the existing situation may demand something else.
You may not have time to do anything with your villagers yet, because it is probably more important to micromanage the two main battles that you are engaged in as the scenario starts. The southern battle needs your attention most, and right away. You have 8 Axemen against 8 Axemen and 2 Scouts. Obviously, you don't want to fight a battle like this. In the northern battle, you have 6 Axemen and 3 archers against 5 Axemen. Three of your Axemen, and maybe two enemy Axemen, in general won't participate in this fight. This battle is strongly in your favor. Now it might seem that you ought to try to fight both battles at the same time, but that's not what Napoleon would do.
After you've started the scenario and had a look around to see what's going on, restart. Immediately jump to the south battle, select all your troops by double-click or box scroll, and run like mad to the NE. Don't run straight north, because that's right into the middle of your villagers. Some of the enemy will pursue, but only the Scouts can catch you, and they don't do very much damage to same-tech infantry. Assign a control group as soon as your troops are moving. Then jump to the north battle, and get all your Axemen into the fight. Assign another control group. Your archers are doing fine by themselves, so leave them to the last, but assign them a control group as well. Crush the enemy in the north and then crush the pursuit from the south. As soon as you get a chance, pull your wounded Axemen out of the fight and reorganize the troops. However, some enemy Axemen are probably beating on your Houses by now, so rush the troops back over there and save your Houses. You should probably send a villager as well, because Houses don't last long under attack. Hunt down any stragglers in the south, then hunt down any stragglers near your Town Center. Then put your villagers to work.
Your archers are the key to these battles. The enemy melee units want to beat on the archers, so your melee units get a lot of free hits on the incoming enemy troops, as do the archers.
Because you have concentrated your forces against one threat after the other, using your INTERIOR LINES OF COMMUNICATION, and used COMBINED ARMS, you should have been able to really do a job on your enemy. Killing 15 enemy units for a loss of only 4 is not an unreasonable result. Not only that, but Hannibal seems to love sending villagers right through your base, and you can pick them off for free. You should have got 2 by now, and the scenario is only 2 minutes old. Save the game now and pause it and think. If you epic-failed, and your position is a shambles, restart the scenario and do it right this time. In any case, it is important to not get over-confident here and to relax, because Hasdrubal will keep the pressure on for a while yet. He knows that if he doesn't beat you in the first 5 or 10 minutes, he won't.
Have a look at the Achievements again. You now have 7 villagers and (say) 13 troops. Hannibal has 7 villagers again, because his new production is dead. Hasdrubal has 10 villagers and (say) 12 troops. So you have made definite progress.
From this point on, you must expect the enemy attacks to head straight for your villagers, or whatever looks weakest. The AI does cheat, and it knows exactly what you have. You really want to have a wall-in, but that is not feasible yet.
Hannibal appears to be in the NE (that's where his villagers came from), and Hasdrubal might be in the south. A good place to put your first Tower is south of your Town Center, near your Houses. They are very exposed - don't build any new ones over there. The best place to put your second Tower might be north of but close to your forage area. Station half of your melee infantry near each Tower, and the archers in the middle somewhere. One thing you should never do in a situation like this is build a Tower (or anything else) on the fringes of your detection zone, because a single enemy arrow can cost you an awful lot of resources while the building has only one hit point or so.
You should already have found a substantial gold deposit, so you should make a significant effort to get a Cavalry force into action ASAP. Accordingly, your Axemen are all unimportant now, and there's probably not much point in getting any new ones.
Specific unit production targets for your next House are 3 new villagers and one Scout. Allocate your existing villagers appropriately to accomplish this. Specific unit production targets for your next House are two Cavalry, two archers, and one Scout; allocate your villagers accordingly. It is possible to produce past the population limit in AoE if you have more than one production building.
The next attack consists of four infantry and a catapult, although the catapult shows up later because it is slower. This attack was probably already programmed at the start of the scenario. The infantry shouldn't make it past your Tower, but the catapult might be a bit more of a challenge. Your first Scout might already be available, but if not, you will need to rush the catapult with Axemen, not the ideal force for the purpose by any means. It's time to start laying down a wall at the south side of your base.
The third attack is a single Scout, which isn't a problem if you see it soon enough, especially if you already have a Cavalry. After that, all attacks consist of about 5 of the best available Barracks infantry, with or without a catapult.
By the 10 minute mark, you should clearly have the dominant position. Hannibal might be down to just a couple of units. You should have 5 cavalry, 5 archers, 10 obsolete infantry, 10 villagers, and a priest or two, plus Towers and walls. Hasdrubal will have only about 15 units, of which 10 are villagers. There is no question that you are going to win. The question is how messy it will get.
The enemy attacks will come in from any direction. As long as you see them coming early enough to rush your cavalry and archers to the threatened sector, there is no real problem. But what if they park the catapults outside one of the forests flanking your base and shoot over it? Then the first warning of an attack may be when a villager dies.
There are only a few solutions to this problem. The interim solution is to have a bunch of Scouts out there to give early warning of an attack. The long-term solution is to push your walls forward so that there are no soft targets within catapult range of your wall.
There is an important scenario bug. Hannibal must pass a villager right through your central base at the beginning of the scenario, and he will either succeed, or die trying. It is very easy to kill these villagers off, but if even one gets through, he stops doing it. The villagers are sent in pairs, and if one pair is killed, the next one is sent immediately. Hannibal will gut his entire workforce to send those villagers, and if he runs out of food while doing it, c'est la vie, c'est la mort. Obviously, it makes a huge difference whether you face one enemy or two. Perhaps the scenario designer thought that if you stay in the middle, you should only have to fight one enemy, but if you abandon the center to set up camp somewhere else (why? where?), then you should face both enemies. In other words, if you let Hannibal and Hasdrubal link up, then Rome is in trouble, but if they can't link up, then Hannibal is in trouble.
It's not clear exactly how far Hannibal's villager needs to get, or exactly what he needs to do. In any case, if Hannibal stops sending those villagers early enough that he still has a food income, then he can rebuild, and pretty soon you will be facing serious attacks from two enemies. If this happens, and you can see from the Achievements menu at about the 10 minute mark whether it is happening, then you will need to fully wall off the north side of your base and build a fleet to guard the river crossings.
You should have detected the river to the north of your base by now, and probably the two nearest fords, and maybe some of Hannibal's Towers on the north side of the river. It is easy enough to wall off the NW ford, but the NE ford poses a problem because Hannibal's Towers can reach across the river. You will need to get a catapult into service to blow away those Towers before you can wall off that ford effectively.
The rest of this walkthrough assumes that Hannibal did not commit suicide. Obviously, if you can beat two enemies straight up, then you can easily handle the situation where one of them has committed suicide.
Once you recognize that Hannibal is coming for you, you need to move fast. You will definitely need more villagers, although by the time you manage to get 15, the tide should have swung in your favor, so you may stop there. Wall off the NW ford completely, but don't build any Towers there, because you can't protect them from catapults. Wall off the NE ford as much as possible, but stay out of the range of Hannibal's Towers. Build some Towers over there; you are going to leave an opening for your cavalry to get out. Get a catapult ASAP (a lot of wood is required) and blow away the closest Towers, and then complete your stonework there. Add some walls and Towers in the south. Upgrade your walls and Towers as much as you can.
It is unlikely that you will be quite ready in the north before Hannibal attacks. Perhaps your un-neighborly activities provoke his attack, but then, he started all this anyway, didn't he? The first wave is three Cavalry. However, you should have two Cavalry, two priests, and 5 Axemen available, plus a couple or 5 of Towers, with 5 archers on call. The priests take over one Cavalry, and then the other two don't last long. You might lose an Axeman. Har, Har.
Your two wall openings should be two spaces wide. You can make gates with two good melee units standing fast side by side. These will first be Cavalry, and later, Academy infantry. You will need about 4 Scouts in the countryside south of your base to give you advance warning of Hasdrubal's attacks, in particular the catapults.
When the north bank of the river has been certified to be free of enemy units, build a dock and then a fleet. Five warships is plenty; you will find that this river doesn't really go anywhere. Your fleet will probably be busy for a while, but Hannibal's casualties should be too heavy for him to survive. When your fleet (War Galleys by now) has done as much damage as it can by itself, produce a Transport and cross the river with your catapult, blowing away the remaining Towers near the fords. After that, hide your catapult somewhere. You have a very small territory, i.e. the front lines are very close, and catapults love to blow away friendly units.
The writing should be on the wall by about the 45 minute mark. All of Hannibal's attacks should have been smashed, and if you've killed enough repairmen and scouts, he won't have any units left. The AI is weak in this regard. It considers repairing and exploring to have the highest priority, and it will strip its workforce entirely to keep those two functions going, and it usually runs out of food and villagers in the process. Hasdrubal still has some power, but less than yours, and you have not yet begun to fight. Your Axemen should all be disbanded by now, leaving you with something like 15 villagers, 4 Hoplites, 5 Cavalry, 4 Scouts, 5 archers, 4 priests, 5 War Galleys, a Transport, and a catapult.
Leave two of your War Galleys at each ford, and explore the river with the last one. You can't go far to the left. On the right, you find a third ford, guarded by more enemy Towers. Catapult ... kill!
With Hannibal out of the way, you should be able to send one Scout to explore the map. You will have run out of gold and stone by now. There is no shortage of resources on the map; the question is, where can you exploit them safely. Your best bet is on the north side of the river, because it will be very hard for Hasdrubal to cross the fords. Of course, you could simply add a bunch of Chariots to your existing forces and finish the scenario that way.
If you happen to find some poaching going on, put a stop to it with extreme prejudice. This is another weakness of the AI: it will insist on hunting, even though the wildlife is under the protection of your army. If you do it right, you can bleed the AI dry this way.
Hasdrubal probably has run out of natural food in his base by now, and insists on hunting rather than farming. Accordingly, you should be able to wipe out all his villagers, and then he can't build new troops. There is no guarantee of this, of course, but you can win in several ways, including building a Wonder.
There are several interesting features on the map, but you will probably not come across them in the normal course of events.