Toned - Like Ice mentioned, have you done this after the fix where you can't really nuke him from the air?

The grouping up is a bad idea because the frost from the Wyrm hits the group and everyone will take damage. Spreading out will make it so only 1 shaman gets hit.

My tank usually faces to the left/right so when I'm knocked back, I won't be out of range of the totems, heals and the frost patches. Using Frost resist so the shamans won't die may help.