That first boss in RFC is hard for any team that uses quest reward gear (12k hit points & hits like a truck). I've wiped with several teams on him, and some teams just can't get past him.

The only advice i can give is
1) keep the tank alive. don't waste mana keeping him at 100%, and be sure you're using thorns on the tank.
2) kill the adds first

if your tank & dps are averaging at least 20dps each, you should be able to to clear that instance. Maybe get some +intellect gear for the healer.