Release everything but slate, stack up, and AoE the crap out. Soon as whelps are dead.. kill lowest dragon>second lowest dragon and last dragon. Kill order does not matter at all. Slate remains chained the whole fight, pointless to release him.
We are using 4 healers, 2 tanks and 4 dps for this fight. Altough its posseble to 3 heal it if all of your healers are in ~359 gear.