Brandt (Ranger) The only reason I have him as a ranger is because he's my most powerful character with a bow (fully upgraded in Urbeth). You can use him as a White Mage (recommended if you're having trouble) but he needs the Cure and Raise spell.
Jusqua (Black Mage) Jusqua needs only three spells: Blizzard, Aero, and Fire magic are NECESSARY!!! If you're feeling lucky with your AP amounts, bring the -ga versions of the spells (Firaga, Blizzaga, and Aeroga).
Yunita (Bard) She must have leveled up the Bard crown at least once so she has Motet and Ditty (I can't remember which one she learns from leveling the crown, but Motet is the only one that you need). She will also need the Cure and Raise spells. Aire (White Mage) She's the tough one, I found that having her White mage crown at maximum helps because she learns the ability "Miracle" Which fully heals and removes all status effects (Except death!) from your characters. But it's a costly 5 AP, but helps if multiple characters need healing and status effects removed. She needs to have the Healthgiver ability, Cure spell, Curaga Spell, Esuna Spell, and Arise spell.
Then, do the following:
CHARACTER - ACTIONS Brandt - Start with boost, next turn Cure, next turn Cure again, repeat. Yunita - Start with Motet, next turn Cure, next turn boost, Motet should have run out by now so repeat. Jusqua - Start with Blizzard, next turn opposing element, next turn use the opposing element, repeat. Aire - Start with Healthgiver, next turn Cure, next turn Healthgiver, repeat.