I beat most of the bosses by having totema's ready for every member. Instant wins on every battle. I only lost 1 person for all 3 of the final battles.
EDIT: Plus Marche is a full Ninja, fighter, and Paladin, so he has holy blade, double sword, beat down, bonebreaker to counter, and other. He pretty puch does 300+ damage per hit, and has an angel ring which revives him if killed.