Each nail gives 1 Limit bar, just have DPS focus on one at a time (I usually tell them to kill the farthest nail from ifrit and go Clockwise), gather and use the Tank LB3 when he jumps away for hellfire and everyone should be able to survive.

As people have said, the pattern after hellfire has a ton of time between Eruptions so you should have no issues stunning it if you figure it out.