I basically loaded up on single-target Archers with good survivability and support. I had my level 90 David, Waver, someone's Archer!Arturia for support, Chloe, Tristran, and Herakles with his Bond CE as a last resort. Took me two tries and some turns - 15? 16? A high number - each time, but I did it.
I have to say, Archer!Arturia was definitely the MVP in that fight.