I've been doing a little research on the lord marrowgar battle and i think it's easily doable by us... so i'll put here some strategies here based on what i read...

first things is raid composition.
2 tanks
2-3 healers
the rest dps preferably 3-4k ranged dps... the less amount of melee the easier this fight is

3 healers would be preferred for the same reason as Gormak in TOC10 where if one healer gets locked out such as by a bone spike or kobold the raid won't wipe. also because the tanks receive massive damage from saber lash so a third healer would ease the pressure

the tank should ideally tank him where he stands and face him away from the rest of the raid. the off-tank should stand next to the main tank to absorb the saber lash damage... because of the -20% dodge reduction debuff it's best to have a warrior or pally main tanking and a druid geared for high stam absorbing saber lash.
all dps and healers should spread out behind him far enough to prevent any 2 people from receiving bone spikes but close enough so everyone is within range of the healers... the raid damage is minimal but can get overwhelming if people are careless.

His abilities are as follows
Coldflame- he periodically summons a line of fire directed at a random player which ticks for 6000 damage per second. despite being 'fire' it actually does frost damage so it can be mitigated with frost aura or frost gear but ideally should be completely avoided. if your not confident enough to avoid this fast enough then wear your frost resistance boots or belt for that extra frost res, but the flame most quite slowly so it's not hard to avoid and also DBM gives u plenty of warning

Bone Spike Graveyard- He throws a bone spike into a random area and impales a random person... this is the reason why we want to be spread out to avoid too many people being impaled. the dps will need to shift the focus to the person being impaled and quickly kill the spike especially if it's a healer thats impaled. 2 ways to do this is to either have 2-3 people responsible for killing the bone spikes or just have the person being impaled shout out on vent and dps constantly shift their focus

Saber Lash- deals 200% Melee damage spread between the 2 tanks... i suggest having high stam tanks to provide a good buffer zone.

Bone Storm- every 30 seconds he enters his second phase where he does a Bone storm. this is like a warriors Bladestorm where he spins in a whirlwind but does pissy amounts of damage.... where it's dangerous is that he also summons coldflames spreading away from him in 4 directions so when he enters this phase the raid will need to pay extra attention to where they're standing to avoid coldflame damage... after this phase everyone will need to go back to their positions, ie tanks together facing him and the raid spread out behind him... from what i read and seen this phase transition is the hardest part of the fight as either the tanks are not close enough together and this one tank eats too much damage from saber lash or the dps dies from coldflame damage...

so in short, this fight is a heal intensive fight that requires lots of raid awareness and movement to avoid as much damage as possible