You really want one hunter to dispel Enrage from Shambling Horrors which are tanked by you (prot-warrior), otherwise you should get some stun rotation going to make things easier for your healers. You also might want to take second paladin for additional blessings.
I would say have your current warlock be demonology, take the ret paladin and the elemental shaman, this will help you out, since enhancement shamans and retribution paladins use spell critical strike and spell power to increase their damage.
For stuns in seconds phase.. you have a warrior tank, no issue.
Phase 1 wil be most tricky with the shambling horrors, but when we do it on 10man, the warrior tank on shamblers stuns the first shambler untill it dies, and I tranq the second, what you could do is just have some other stuns/cooldowns go in, like a hammer of justice.
For phase 3, it helps to have paladins with aura mastery to help deal with exploding Vile Spirits. Also have your offtank soaking them as much as possible, so most of the damage is focused on single player with high hitpoints and plenty of cooldowns. Position LK to far edge of the room and soon as he starts channeling Vile Spirits, have your tank run straight across to other side with melee to put as much distance as possible between yourself and Vile Spirits. Offtank stays around middle and tries to intercept spirits.
Frostmourne room is basically 3d version of space invaders and your whole raid gets ported in, you have Wicked Spirits coming down towards the raid that you need to kite while avoiding black/purple bombs that are dropping from the sky. Mark one player to guide you through and follow his lead while ranged nukes down Spirits. Soon as you get ported out, spread out for Defile.