Disrespectful step children

How do you go about dealing with disrespectful step children. They deliberately disobey me. My husband doesn't say anything to them until I've just completely lost my temper. They have smart mouths and do nothing I ask them to. In fact, they do the opposite then tell me they purposely did the opposite. They're both under the age of 10. I cook for them, clean up after them, wash their clothes, etc, etc, etc. I'm not expecting them to understand what I do for them, I'm expecting respect out of them. They broke my couch after asking them multiple times in one day to not jump on it. I don't discipline them and apparently neither does my husband. Idk what to say to him bc he either gets offended that it bothers me so much or just comes back with "they're just kids" or "they don't intentionally do these things" HELP!! I'm about to have a breakdown. I'm 27 weeks pregnant and my hormones are a roller coaster right now, just to add to it. 
Might I also add: I've been step mom for 3 years. They have a step father as well. So they aren't new to it. I've tried chores and rewards. I've tried individual time alone with them and going above and beyond to show them I care about them both!