Hey,

For Marrowgar, make sure your two tanks go in together and turn him. The rest of the raid bunch up on his butt. If you do that, the flames will shoot at the tanks and at that point all they need to do is strafe right or left. This will allow you to focus fire the bone spikes faster and for the players with the biggest health pool to eat any flame damage that may occur while moving away from it. The damage during the bone storm is negligable, all people need to do at that point is not freak out and stand in flames. Agro drops at the end so it's important the two tanks stand together at all times and be prepared to taunt at the end of bone storm.

Good luck