Off the top of my head, a decent way to secure victory would be to simulate the fight against Wiegraf (the cheap way). Go in with Ramza as a squire, sub Steal. Give him Auto Potion, Defense Up, and Move Hp up. Equip him with Excalibur, Escuchien 2, Judo Outfit to prevent Death, 108 Gems, and doesnt the Thief Hat prevent Stop? I know theres something you can equip in the head piece for a guy to prevent it.

Start the fight and just start Yelling. The first few turns really decide this fight. I think the idea would be to Yell and move away from the Assassins (nothing you can do about elmdor), until you easily have 3 turns between assassins, then move in, kill one, and move away again. Do that till Elmdors alone then pray you can steal quick enough before your pots run out. Note in this setup you CAN still be confused by Muramasa and charmed by the assassins, all you can do is hope they dont cause them enough to prevent you from regenerating health back from damage.

Thats the only way I can think of doing it.