Most of the guides now are cheese method. For that method to work you have to burn boss and tiny atro before mechic happens.

Back on helping.

What is bigboom you are talking about?

When did everyone die? What kill.them?

It's hard to say anything without actually seeing how things are happening, but several moments that caught my eye... First, if flames from atronachs clutter the place, then you may be too slow to burn the boss. You have about 90 seconds from engagement to burn him to 75% to avoid the curse, then another 90 seconds to 50% after the tank have collected the adds and walked them away, and yet another 90 seconds to burn him to zero. If fight takes long enough for people to get cursed between add spawns, the probability of wipe skyrockets.

Second - the reach of his AoE isn't infinite, tank is supposed to avoid being pulled (more so because, with the tank, his adds will end up in the middle of your group too), for that the tank will have to go rather far away - across the lava river and a bit closer to the stone staircase (if you're burning the boss near the entrance). For that reason, tank also usually can't see the boss' health, so you have to inform him when blast happens (the jumping health of whole group is also a good indicator). Blast is not supposed to kill you, but it does leave whole group with very little health, and if you're already standing in fire by then, it's most likely a wipe; make sure you don't get additional atros and fire circles, and heavily lay down the HoTs just before the pull-and-blast.

The fight is generally teetering on some good timing and a bit of chance when it's done like that, so it takes a bit of getting used to, don't let the failed attempts discourage you.