Maybe you can have a tension gauge in the game for each character. You have to keep them calm by yelling out things to reassure them or get them riled up for battle.
But as soon as they reach their breaking point, they start to act all wierd e.g. whispering to themselves (which could add to the games atmosphere), might turn on you, give you up, use you as a shield or run away leaving you hangin' in the middle of a firefight - you get the picture.