The Mafia Game

Have you ever heard of the Mafia Game?

12 players.
3 are mafia who work together to kill one person per night
1 is a medic, who each night picks one person to keep safe from the mafia's grasp
1 is Cupid, who links two souls together, meaning when one of the linked dies, they both die.
1 is a vengeful civilian who, upon being voted out or killed will kill one person with them.
The remaining 6 are normal civilians living their day to day lives out with no special abilities, hoping to stay alive.
No one knows the others roles. That's the fun of it.
Every morning, a vote is held by everyone, and they must decide who their think the mafia is, and they will be executed.
The Mafia win if #of mafia remaining= # of players remaining
the civilians win if they vote out all the Mafia.

Everyone must work together. the Mafia with eachother, and the civilians with eachother.

But how will this work when a few of these players aren't working for the good of the others?