Two heal it, you're a holy pally. That means you can carry the fight really hard, in fact if you have enough gear you can solo heal with ease. There is ZERO need for 3 healers. Also weather 2 or 3 healing make sure the Disc priest is smiting at the start, it's free damage. I can check you pallies and priest so here goes:
Prot Pally
1) Gems should be yellow - mastery, blue - mastery+stam and red - mastery+parry OR all mastery.
2) Reforging is non existent, get more mastery at the cost of expertise and hit
3) Spec is terrible, use this one
http://www.wowhead.com/talent#sZGMhsRddoRucbG
4) No glyphs at all
5) Start using SotR when 3 HoPo is up, it'll vastly increase his DPS (which right now is way too low)
Holy Pally
1) Unglyph LoD for this fight
That's all I got, seems in order. Make sure to take red and blue buff (letting the other healer do green) and carry heals. Save CDs for the last minute and then spam HR non stop with blue
Priest
1) If you 2 healing it stay holy so that there's more benefit from green
2) If going disc then get Atonement and smite for the first minute of the fight, it helps on DPS a lot.
But your primary problem is DPS doing way less than what they should in that gear. With their gear they're all capable of at least 25k, some upwards of 30 and yet they're being beaten by tanks and dropping to below 20k a lot. I honestly don't know how this is happening but they need to play way better, even if you kill Ultrax you'll wipe on Gunship for months. Ask for individual help on the class forums and just... focus more?