You seem to have everything under control so I'm not sure what you are asking.
Hunter Frost Traps work well and Lich King triggers them and makes them become active so even if your hunter gets picked up its already down.
Just spread your slows out, rogues can weapon swap to an OH w/ crippling during this phase, you have 3 SP's, you could even make an Arcane Mage pick up slow and you could double up slows on every Valkyr.
Ret PLD aoe stun when they come down, then have the second stun happen when they are like halfway out then have a third stun on them if/when they get closer to the edge. Just let people know which stun they are on each target so they don't go DR as soon as they land from everyone stunning everyone of them.
Also are you aoeing ahead of time right before they land? That helps alot except for the 2nd one where Defile lines up right behind it. Having everyone going all out AOE right before they land puts alot of damage on them and allows ppl to then find their target after they are marked and they can keep AOEing if they all fly out together or switch to single target if they fly off in different directions.