This is one of the two boss fights in the game that are difficult to multibox with a warrior tank. The biggest problem in this fight is that the mobs will charge/stun your warrior and run past him before you're able to pick them up. To fix this, place an armored dps (shaman will do) at the door, in front of your warrior. This will make the mobs charge-stun the dps instead of the tank. After the mobs have charged the dps, use your warriors thunderclap to pick them up.

Brann can be healed, so heal him when he gets low on health.