Well, deathwing or neltharion is a huge difference because one realm is wotlk and the other is cata.
Im not very experienced when it comes to raiding on cata so ill only talk about wotlk.
If ur goal is to really raid ICC 25 one day than u need classes which can be multiboxed to full potential.
Mage: Arcane mages have a easy rotation and can be multiboxed to full potential.
However in high end gear pretty much every mage switch to fire or frostfire because it pulls significant more dps.
I dont see how its possible to master the instant pyro procs so I doubt that its possible to multibox fire mages to full potential.
Moonkin: Its impossible to perfectly master the eclipse proc as multiboxer. I would stay away of moonkins.
Affliction Lock: Affliction has a very complex rotation which involves shadow trance procs for instant shadow bolts. I dont think its possible to perfectly master their damage rotation.
I would rather multibox demo or destro locks because their rotation is much easier and they pull anyway more dps.
In general ur team is missing strong damage dealer.
U definitely need to add MM hunter and shadow priests.
Both classes can be multiboxed to full potential and pull the highest dps.
Also, u are mixing mdps and rdps which can make things very complicated.
Might be better to have only rdps so nobody beside the tank stays close to the boss.
I would change the setup completely:
Tank: Prot pala and Blood DK
Tank healer: 2 holy pala
Raid healer: 1 resto dudu, 1 resto shami, 1 disc priest
Rdps: 1 demo lock, 1 arcane mage, 8 MM hunter, 8 Shadow priest
Mdps: None
With such a setup u would have pretty much every raid buff except +20% melee haste and +5% physical crit.