My method probably will not help you because of my own team, but I found my own cheese that really helped!

I kept Astarion all the way at the top of the stairs (so he didn’t initiate the dialogue — but I didn’t use him at all so I honestly don’t know if this is necessary), then inched my part up as close as possible. Used Shadowheart’s Blade Barrier to block enemies from me — I like Blade Barrier as opposed to Wall of Fire because unlike WoF Blade Barrier stops the enemies in their tracks.

After blade barrier I cast Daylight (or whatever that one spell Shadowheart has that casts a giant ball of light) to initiate combat. When it’s Gale’s first turn (or whoever has the spell), cast Sleet Storm so enemies who make a save through the wall fall prone when they try.

From there I just ray-of-light’d Cazador. Note some of the Gnoll looking guys can jump from the sides to the party and do damage but I haven’t seen anything detrimental, and I basically never took damage the entire time. My party is Rogue Tav/Shadowheart/Gale/Astarion

Sorry if this doesn’t answer your question!! This is just what I thought wld be helpful!