what we have done on this fight is left our sentinel on Withering Horror all the way through the fight. We have two range dps, sage & commando, they aoe down the little adds in the blood pool. We put one healer in the pool first, then we put our second healer in the pool. Our second Melee DPS(Shadow) waits on the boss until the tank has the Male in place near the healer in the blood pool. After that, its a a rinse and repeat. We do not do tank swaps until the mails spawn, loss of threat in this fight for any reason causes additional adds to spawn so you need your highest dps'ng tank to start off the fight and use power adrenals, etc. Ours even puts his power relic on, clicks it, then swaps back to his defense stat relic and runs into the fight. We are nearly BiS 63 now, but we can almost beat him before the third pool, we stop dps on him to finish third pool to avoid Twisted Spawn at 13%
This video is from our Gunnery Commando's perspective. Maybe it will help.