Suggestions for my PVP Team

You've got the majority of a nightsister team. I'd stay the course, running Ventress as leader, Talia as mid range dps, healer and turn manipulator, Nightsister Initiate as heavy damage and tank, and then go farm Old Daka for stuns and low healing (and sometimes res). Running this team would have you attacking blazing fast. To cram in a little more, I would consider Captain Phasma to double your teams damage potential with advantage and through turn meter manipulation. This is also an all darkside team, providing you with a lot of strength when doing darkside missions.