Well would you have guessed it. It seems the Cardinal is a traitor too. In fact, since everyone seems to be on the wrong side, but somehow, the same side as each other, it would appear that Ramza is actually the evil one causing unrest. Or something.
I’ve managed to rescue Mustadio (or whatever his name is) today, then rescued Agrias, all without too much difficulty. They’ve now joined my party “proper”, rather than just be uncontrollable guest allies.