Simple. The bosses don't leash when you move out of their room, so you just pull them all into one room.
You'll have to keep in mind the mechanics of each fight;
Archavon will grab the primary aggro target from time to time.
Archavon will jump around and leave clouds to not stand in.
Archavon will throw rock shards at a random person so ranged should be spread out.
Emalon will cast Lightning Nova so he needs to be away from ranged people.
Emalon will charge one of his four adds and it needs to be zerged.
Emaon will chain lightning people so ranged people need to spread out
Koralon isn't out yet, but once he is, you learn and master his mechanics. Remember Koralon will have the most health of the three and will hit hardest, so you'll have to decide which pull order you start with or if you just pull all three at the same time. Also need to be careful on how low you get each one. Archavon can be killed extremely fast, Koralon will take the longest.
This will probably be done with an "abnormal" raid comp such as using 3 tanks or 4 healers on the 10-man version. It'll be about coordination and properly dealing each of the abilities.
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