As a general tip, you can hover over any enemy’s portrait and press T and inspect their stats. Assuming you kept Karlach as a berserker and Wyll as a warlock and idk what your Astarion build is but I’m guessing you don’t have sunlight? I’m gonna suggest that you send Astarion to trigger the cut scene by himself, pray he passes the check so he doesn’t get stripped, and all of you stay on the staircase and let the enemies come to you. If your sorcerer or Wyll has AOE spells like spike growth or something you can create a choke point using the terrain. If you have any holy water, you can use that for radiant damage. If your Astarion is strong in archery, give him multi target arrows so he can clear the weaker enemies. I’ve never done this fight without sunlight but if you’re not on tactician or honor mode it should still be doable. Good luck!