As long as your struggling with your DPS (as you are), ALWAYS assign ALL healers to the pheromon kiting rotation and start it of with your tank.
We got our first kill when all healers were kiting aswell as our both usual tanks went offtanking in dps-specc and -equipment, aka: We were maximazing our dps even at the risk of people dying in some attemps.
After your dps is high enough (comes naturally with experience/gear), feel free to assign more dps and less healers and/or switch one of your offtanks back to full tank mode for tanking the furious swipes.
At least that's what worked best for us.