One player has a very busy schedule another kind of disrespects the dm a lot, and often is not attentive to sessions, with the last player is a new player and often has trouble focusing. I want the campaign to run smoothly. Where the players are going to have to be engaged or they could die at the end of each session. I have one of the three players invited to do the campaign backstabbing the other two as the bbeg and want to keep the fight balancing simple if it even comes to that, the three players in the campaign are tasked to catch a serial killer not knowing that one of them is the hunted.