No no, thanks for your ideas :)
I do want to find a way to have people be more involved with each other. Maybe if there was a reason why working together would give you an advantage somehow, but I still want betrayal to be a realistic option.

I don't think I will let Gods or angels play a huge roll in this story, I don't even know if they should exist. Maybe this is just some crapsack world where there is only 'evil' and 'absence of evil'. 
Otherwise, this will be some kind of game angels either aren't aware of, or have no jurisdiction over. (Since every participant agreed to play the game) But who knows, depending on how the story goes, they might just show up...
Demons might make a short visit, but they don't have anything to gain or lose by hindering or helping the players.
Most demons would agree that seeing humans destroy each other is way more fun than destroying them yourself.