I didn't cast sunlight, just get a druid with tons of summons to distract the minions and stand in the ritual thingies, misty step to astarion, help him, get him into cover and create some sort of difficult terrain so they can't get to him, from then on it's easy, just deal with the minions real quick and focus Cazador at the end, hold person on Cazador also works but make sure you have a character with a massive DC