Like I said, I had tried several times to do this mission with just henchmen, and could almost complete it... which means that the only part of this mission that is difficult and is the clincher is that last team with the 2 priests. That one takes strategy and planning - a team effort.
The first group I was in was nicely balanced. We killed all the sand giants without problem, got thru the first team no problem, second set took a little while - but still quite easy. When we got to the third, we did great on the first team to the right - went on to the next and did ok, then the last we just couldn't quite get. We decided to give it another go with a different strategy (separate the priests), but some left and were replaced by a couple idiots (sorry, but they were!).
So one of them insisted that we not waste time killing giants because one of them was a trap and we would all die (like the last team he was in)! I said that if we can't manage to kill the sand giants then we will never be able to manage finishing this mission (I realize that the giants are just added morale boost, but honestly if a team dies killing them then they might as well not even try the rest of the mission!!). The team listened to the new guys and bypassed/rushed to the hero after only killing 2 of the giants. Rushed into the first team and died (one of the guys had to go quick because he had to go to work!!). So ended that group... several dropped and more were added (not even sure at this point who was leading this group I was in).
This time a guy took charge bypassed ALL the giants and ran straight for the hero. Made it thru the first team, guy rushed us during the second set and we died.
Last try that night... we had several leave and more added. I asked what we were doing this time (fighting or running

). Some tried to run, but others stopped to fight. I asked again what the plan was. The monk logged, so I bailed. By this time it was 10 pm and I had enough.
I personnally don't care if the giants die and we get morale boost (even though it is easy extra hps/energy). Just want to have a group that takes it step by step and thinks first, hee hee. If the first group I was in would have stayed together, we could have done it I think. I loaded dodge and was ready to draw most the mob away while the rest of the group worked on getting the priest dead. Not sure if that is the strategy to use, but it could work?