Gotta bring an enchanter with you next time, have them mez both mobs then cast all their debuffs on them (slow, ac, mr, and str debuffs), memory blur them (brutal if they went after enc), then engage with melee. Recommed 2 groups with 3-5 tanks in each group plus cleric and possibly other miscellaneous classes.
Also have a necro ready with summon corpse in case anything goes wrong (need 12 coffins so make sure everyone brings one)