I think something that may help is you can respect Shadowheart to lifedomain, all the healing abilities really helps keep your team alive plus radiant damage does very well here. Second, if you are using Gale using fireball to clear the little brain guys also helps. Third, before you go down to confront the boss battle there is this blue thingy that heals you, cannot remember if it restores spell slots tho. Hope this helps and if not could you please post screenshots of your character builds? This would help me give further advice, good luckl!
