It helps (obviously) to have a high earth resistance and make one of your guys carry a shield. Once you get within melee distance the earth elementals switch to a melee attack which you can block.
I usually had one guy with a shield and high earth resistance running straight at them (causing all the attack to be directed at him) and the other one following once everything in sight was attacking the first one.
Or you can try archers using air arrows with sneak and a hit and run tactic.