[@Medili]
Regarding Revenants:
The BOR Parasite question I can't answer because it's part of the discoveries the group will be making. 
New Revenants are still being made but it's a government controlled process. You would need a high level of clearance to be able to access that kind of information. 

Revenants regenerate twice as fast as humans. They still need treatment. For example broken bones won't heal properly if left alone. Feeding while wounded speeds up the process by a lot. 

The Lost have the same regeneration speed Revenants do, since they are former Revenants. They will survive the complete destruction of their body and that's why they're so dangerous. They disperse like Revenants and come back, the time this takes varies, but it's not instantly. 

Regarding Sidhe:
They bleed, but their blood is not the same as humans.(the exact composition we will figure out later) They also heal twice as fast as humans. 

Regarding Humans:
You are right about both. Humans are fragile in fights because they can't come back from the dead, damage they take is usually permanent. I added humans as an option, in case anyone had a particular character idea in mind that would fit them the best.