Did you prebuff your party: bless, shield, and haste work wonders. Also, make sure you get help from the Avernite soldier and the giant rat if you have enough nature lore. Don't be afraid to summon a couple shades to act as things that can absorb some damage and deal some as well. Another thing is a basin that gives you essence armor is nearby, drink that. Finally, items: use them.
EDIT: One more thing. Using leg sweep helps out a lot too. Shield breaker is more effective when there are three of them.