You are supposed to walk on the steam that is not active, look closely as it's hard to see sometimes. I hope this instructions are clear as i can't tell you in a different way..
I just killed them with an axe whenever they saw me. I didn't even stand on a box. All you relly need to do is hit them once when they charge at you, once they're down all you gotta do it hit 'em over and over again. Untill it stops moving.