Tank should grab the middle one, and kite him in the room behind. 2x dps + heal should stay in boss room, killing the medic and rupting everything. Massey can walk around if he want to, dont care about him at the beginning. After killing medic, kill Massey. They should be enrage allready, but Massey doesnt 1hit anyone:) After killing Massey, go to your tank, and dps him slowly down, dont try to follow the boss during the kiting, just stay on distance and kill him slowly!
GG
Killing him in 1st try now with this