A Couerl alone is waaaay easier than more than one, though. You can basically just get behind it and keep wailing without it even doing much to you.
When there's more than one you can't just do that because the other one is running around doing it's damaging AoE. The insta kill move is devestating to the AI too. While you can be smart enough to not run at it while they sit down, the AI blunder in like fools.
Either way, I recommend tanking up with defence food and getting some Phoenix Downs just in case your team mates go full retard. Also make sure you just watch out yourself that you don't run into them while they're charging up the insta-kill.
Ahh, I see. Cool, thanks.