Most definitely a DPS issue there. Our group pushes 1 ghost with 4 DPS and have done it since our first T9 clear. Make sure one of your bards is battle voicing foes and everyone is using stat potions as soon as Nael drops after megaflare.
Aside from that it sounds like you all are close. Keep calling out mechanics and encourage everyone to be vocal. You'll have it down soon.
