The kneeling man to the left
He is carrying a seal belonging to the seven seas company. According to the letters on Nicolas and Angus, the director of the company is Dr J.T. The list on Nicolas gives his full name as James Turner.
The standing man
This is a familiar face, Lazarus Herst.
The man with the crown
The man with the staff
It might be a bit difficult to recognize him, but this is a reoccurring face. The letter he carries makes it clear that it is Walter Keene.
The man with glasses
Another familiar face, this is Nicolas Maker.
The dead man
Figuring out the identity of this man requires solving why he died. Going by the scene as a whole, and the scrolls in the chest on the boat shows that a miracle was attempted. And one man seems to be in charge of disproving miracles, Angus MacBain. It seems like he failed to repeat the miracle and died in his attempt.
The letter on Keene makes it clear that he was being blackmailed by MacBain about how the miracle of flying would be performed by Herst.
Who held the relic
Going by the events that took place, it is clear that Walter Kene is holding the relic right now. He retrieved it from Angus MacBain and it belonged to Lazarus Herst to begin with.
Filling out the scroll
Once you've understood that someone attempted to demonstrate a miracle and someone else then tried to repeat the miracle it becomes rather obvious what took place.
It was Lazarus Herst who demonstrated the miracle of flying by jumping from the lighthouse.
As per tradition, Angus MacBain tried to replicate the miracle, by also jumping from the lighthouse. It didn't work for him so he died from a head wound.