Well, the strategy i have seen and done but failed each time:

8 Man Party (Duh)
2 tanks - 1 MT 1 OT.
DPS - 4
Healers - 2

Tanks - 1MT other OT.
DPS - Focus Garuda, Then focus plumes
WHM/Sch - Focus MT, party heals if needs be after % , 1 may holy to help but shouldnt be needed with the correct people.

Phase 1 - Same lv44 Battle except for 3 teleports, N, Mid, E.
Phase 2 - (Ends at the reckoning) - Gather at NW, 1 MT for Garuda, 1 OT for 1 Sister, DPS flame other sister, healers use Medica II and then focus heals when safe to do so, if not, use Medica II and save shroud for this moment due to healer aggro.
Phase 3 - Gather Mid, focus garuda, focus sister spawn, Medica II heals, flame green sister, flame red. flame garuda.
rinse.

Thats what ive seen mostly.. + id recommend Darklight gear to a high degree.. lv45 relic just doesnt have the defense or stats needed. + Ifrit/lv50 weapon.