F. Coffin Moogle and Ayama should be plenty to keep you alive on EP stuff in say Ceizak or Yahse. Considering the low base damage on trial staves you're not gonna be doing a ton of damage anyway even with shattersoul. SMN would be a little squishier than SCH but you should be able to have your Avatar tank considering you'll be a lower item lvl than them with a 70-75 staff. Otherwise Ayama will probably tank with just melee damage.
Edit: scratch that, I'd use Cherukiki since she won't melee and screw up your SC with a random WS.