You can do this with 5 in 25 man mode but you have to play it like old school days where you kill the drakes as they land. Each drake only hast 384k hp so you can down them really quickly.

Basically you open on sarth pop lust all CD's and burn her to 50% kill Tenebron you get about 40 more seconds on sarth, kill vesp and you can usually kill her after that if not kill the other one and finish her. She goes immune when the portal opens and the third one lands if you are too slow on killing the drake preportal you have to enter the portal with one dps and kill the add in there. That highly complicates the fight but I have done it regularly with: Blood DK, Destro lock, Surv hunter, Ret pally and Attonement spec Disc priest. They are all pulling 30k+ DPS I generally drive from the ret on this one so that I can do decent dps on her. I have 4 piece shadow LFR gear and alot of DPS gear on my Disc so she even does 15k dps.

Avoid the fire waves and the fight is not too difficult. Let the waves hit you and you will most likely get too far behind on healing and wipe.