Well, I'm kinda tired of everyone complaining about the AI and just accepting the loss. (the AI could be - a lot - better I agree, but its not like you can't do anything about it)
So, what did you do to outsmart the AI and how did that work out for you? (please don't say 'grinding')
I go first. - The major problem: AI casting too many spells. I just turn everyone (and I mean everyone ) to "dont use any abilities" and pick a familiar with strong attack and good defense (defense is essential here, so choose it before attack) as first familiar to everyone on your party so each one will always start with that high str/def. familiar.
- Give your best 'magical attack' familiar to Oliver as he got more MP than everyone. Though, balance things a little and give one good caster to each one on your party.
And that is basically it! I almost everytime choose Oliver (or his familiar) to start the battle and begin with a badass spell (preferably an AoE one. Hot Stuff is great at the beginning) while everyone else are using their melee familiars. Depending on what my level is battles end very quickly this way. If not, you'll have to pay attention on each one HP and probably change characters or even tactics so you don't get killed. But that is basic stuff, I'm sure you'll figure out what to do on each situation.
This way your MP will last a lot and, even when Oliver's MP reach 0, you have 2 other characters with full MP. And you can change familiars as you wish so just give that caster to Esther (or Swaine) and you're good to go. Even when them both depletes their MP, Oliver must have some now as the AI is kinda smart to the point they'll look after blue orbs. (though I would recommend that you always keep a couple of chars with at least some MP so you can heal yourself if needed)
needless to say, you might wanna change tactics before facing a boss (though I kinda like starting a boss fight with everyone on 'no abilities'. The best person to decide when and what spell to use is myself so...)