<Snipped quote by Little Bird>
Maybe... Didn't think about that, we could go with one guard and one prisoner per person if they so chose to play both
Ok, here me out-
Don't make something optional where it will create problems; everyone would be required to do both, realistically, because just one or two players playing as guards? Within the setting, these players now have the clear advantage over players who aren't doing that, which could provide some easy conflict, but could also just make the game fall apart due to PVP.
tl;dr: I think that's a bad idea.