A possible extension of TF's idea would be having a fourth category of girls:
Gang Leaders/Rivals. At the beginning of the game, the gang leaders could be randomly chosen from this pool. If, say, their gang was destroyed by another rival gang one of the choices when they came to you could be putting them to work in your brothel or giving them a lieutenants position.
Or it could a trait called Leader, that could be given to any girl. when generating gangs at the beginning, the game could look for the Leader trait and remove them from the pool to act as leaders for the rival gangs.