Have your holy paladin heal with Righteous Fury up so that all the adds goes towards him. Have your bear tank root one and if it's got time before nef is landing taunt an add and let it hit him with Nature's Grasp active to root it. Have all 3 priests shackle adds as they get close to the paladin. I was going to suggest Ring of Frost from your mage but seems like you got a hunter instead. Holy Wrath stuns them if they break and gets too close. Hunter trap works as well.
I'm not saying this is the best option for you, just that you have lots of options which frees up a person so you have dps to push Ony and Nef. You have lots of CC's in your group, you might as well use them. Obviously the closer they're stacked for phase 3 the easier it gets to pick them up but you don't need it to be perfect to be able to do it. This is fairly easy to control with your holy paladin healing with RF. Just have the other healers cover a tank each until adds are down, then the paladin can assist.