Two offtanks should fight the Core Ragers far away from Golemagg. The dogs can't die so there is no reason to DPS them, just keep them occupied. When they are out of range of Golemagg's buff, their horns will stop glowing red. Curse of Weakness can be useful, as the two hounds are not killed themselves. The hounds also can provide a steady stream of health to warlocks via Siphon Life.