well then you are hitting the enrage. i would suggest putting everyone in MoX just to see what's going on and then having your top dps go in red circle after all other dps and top dps stays on boss no matter what. let your other 3 handle adds and jealous males. other than that are they keeping their debuffs up on the boss at all times? not using the right rotations is probably the only other thing it could be unless they just haven't optimized their gear yet. i remember with my sentinel i was trying to get him in BH as quick as possible and ended up with some pretty crappy stats until i started min/maxing. does your dps have to much acc / crit not enough power / surge? just something else to check.
Thanks again for all the good suggestions.
We will try 3 and 1 split the whole time and see how it goes.