Everyone needs wound, morale, power pots and needs to be free with using them. 4 minstrels in a raid still can't keep people from dying from time to time ;p The strategy for this fight is relatively easy to figure out... just executing it is the hard part ^_^ Those fire resist pots you can buy with coins help a little too, but mostly you need the basic pots if you want to win this fight ;p
also your grd needs to have decent gear.... the guard is the most important part in this fight if he doesnt have a full set of mirrored armour or better and stuff then its just that much harder. the grd needs to be tweaked grinded all of his traits and deeds etc.... every bit helps
alot of people are telling turbine to nerf him so we will see...
The trick seems to be splitting the shaman apart using either forced splitting (guard/champ taunts), or letting their normal pathing split them (works better). Once you get them separated/all not healing one target, they're easy.
Also, as with any healer, if you damage them all, they start healing themselves instead of each other, so AE's are good for this fight.