Easiest and safest way is probably to just for all to run to the middle (killing egg or not at this point doesn't really matter) and then Knight use Holy Shield at the very beginning, quickly kill mob while still immune and proceed normally tank taking boss etc. When boss spawns egg kill it and have someone offtank or whoever is strong enough to take care of dog and wait for yellow buff to appear on boss, then gang bang that dog and attack boss untill next big cast, then repeat untill boss is dead. This is more safe way if you cannot handle stronger dog. You just want to keep eye on buff colors and make sure they are yellow, but be careful when buff changes.
If you have strong enough team you can try another way which might be riskier, if buff decides to change at the wrong moment. If boss has purple buff when he spawns egg, do not kill egg at all, so stronger dog spawns and then kill stronger dog right away while boss still has purple buff and continue to dps boss (I'm not even sure if that really matters). If boss has yellow buff while spawning egg, kill egg and dog right away while buff is still yellow and continue to dps boss. If you kill dogs on wrong time, prepare for big damage.
I suppose everyone knows to avoid black circles on the ground and run away from big cast at least and people should barely need any healing during this fight at all. DPS is not really that important in this fight at all either, as neither is with Ice/Fire bosses. Boss will do big rune cast once every 20% either way...
That's how I've understood what's happening, but I'm there just to spam flames while jumping around from one black circle to another...