Yes, they're full HP, and yes, they die in the same single flame blast. Done this several times with and without additional enemies, it's never worked.
Just saw the post. The description implies that all of the critters are found in the same zone, but they're not, good luck? That doesn't make sense to me. I can get over 3 tormented stingers in the Arreat Crater level 2 every time, from the Hell Bringers. So...again, I really don't get what Vasadan means. Super confused now. But, if it's as simple as changing the description of the achievement, something that would take minimal time and effort to change, I don't see why they wouldn't have done that by now.
Anyway, if you two are saying you have the achievements, I guess that's evidence enough that it's not bugged. But I would need more clarification as to how it's done, because I've been doing it exactly right, to my knowledge, and have no more ideas as to how to do it differently. Are there different kinds of demon forges, maybe? If so, I haven't been able to tell a difference...
Edited by Jake#1250 on 6/7/2012 6:04 PM PDT