Trouble with Cazador Fight

So I made to this fight. I know I need to stop the ritual and save Astarion. I tried standing on the ritual spots which disconnects Cazador from that target. But even after I disconnected Astarion and another spawn by standing on the sigil, he still ascended and Astarion fucked off during the fight. I tried using Daylight and that helped a bit. But should I just kill the other spawns? I mean Cazador still aseneded with only five targets.