Husbands family owe us $15,000

Ok so I'm going to try keep this short. Husband and I have been together 9 years and married almost 5. We have two toddlers and I'm a SAHM because our oldest has autism and our youngest will likely be diagnosed in the coming months. They both receive hours of therapy a day so it's impossible for me to work right now. My husband worked for his aunt and uncle at their family construction business when we first started dating. He ended up quitting because the owed him $7000 in back pay. I got pregnant with our first right after we got married and moved two hours away because my husband graduated college and got a new great paying job thy was stable. 8 months later i got pregnant with my second and everything was great. Fast forward two years later and my husband aunt and uncle beg him to come back and work for the family business again. They claim that they're making money hand over fist and that they can pay him three times what he's getting paid right now. I beg my husband not to do it because I saw what they did in the past but some how they got to him and he ended up quitting his awesome paying stable job. It's now been 4 months, they have my husband working SEVEN DAYS A WEEK 16 HOUR DAYS and every week they claim they "forgot his paycheck at home" and they now owe him $15,000 in back pay. We're currently living off our savings (thankfully we have a good nest egg) but my husband is afraid to leave because he thinks if he does they won't pay ever and "you can't take family to court". What the hell do I do here? I begged him not to work for them and I don't want to tell him I told you so but I'm so frustrated he wouldn't just listen to me in the first place.