Fight went pretty smoothly for me.
I literally explored every spot in act 2 and tried to do all the quest so I may have been higher level than others. Chars were level 9 I think.
I did it on tactician difficulty.
Party composition:
*Wyll (mc, default fiend warlock, using repelling eldrich blasts to drop archers from high places to the ground)
*Halsin(moon druid, in owlbear form which is super powerful)
*Wither's Sorcerer (holding twinspelled haste Wyll and Halsin)
*Shadowheart(default trick cleric, spiritual weapon and guardian of faith tanking enemy attacks)
