I need to know whats the issue causing your raid to die before
being able to best give suggestions.
However, off the top of my head, we use 3 mages and 3 locks. This
is the aoe/frost nova team.
Positioning:
We tank Morogrim using a Feral Druid towards the tunnel leading to
Fathom Lord.
2 sets of tanks, one set handle north murlocs, the other set, south
murlocs. Both sets pull the murlocs towards the original spot where
Morogrim spawns. Aoe/Frost Nova commences.
Make sure pallies are quick to BOP and watery grave pple need to be
healed. If MT healers get graved, sound out and have standby
healers take over.
That's about it off the top of my head, hope it works for you!