you can tell the dwarves apart by their eye color from a long way off. Green ones do the toxic cloud. Red are the big strong ones. Blue are normal.
the green ones are very, very slow. they run up close, then stand there thinking about it, then cast the cloud. If you circle them, it will miss, and then they can't do anything for 5 seconds or so -- kill them asap after avoiding the cloud. You can also shoot them as a priority target.

trolls killed with bows at this point in the game.
the burial sites have a lot of skeletons. go slowly, and use the halls and walls and corners to your advantage to avoid bow shots and break them up one by one.