The beautiful humor of this situation is that we feel bad for JOE, who has the business, the money, the responsibility, the stay-at-home wife, the good kids, the camper, and the flexibility to hire the OP's son.
We don't really feel terribly bad for or about Mike, because he's just a lost cause.
We don't really feel terribly bad for the OP, who has the credit card debt, credit in tatters, the five cars (does anyone else see an easy method of reducing the credit card debt here?), the garage full of who-knows-what (EBAY), the part-time job (please think about getting a full time job, you need the $, reducing the financial stress in your life will help you focus on your family, which is clearly important to you), the intermittently-employed DH who is apparently so checked out of this situation that he barely gets mentioned on this thread aside from "he wants the car gone because the police will charge him a fee" (suffice it to say that your DH is not an attorney ... you two have no legal connection to the car ... they can't touch you), the older son who apparently went so wrong that you had to promise your insurance company that he would never drive your cars again (whoa baby), the younger son who is sitting on his rear end for the next six weeks (I'd have him driving Mike to the appointment in two seconds flat), and a five-year-old who is apparently a bit of a handful because the SIL wouldn't be able to handle babysitting.
Isn't it kind of hilarious that we feel bad for Joe in this situation?
OP: as a New Jersey taxpayer who is about to start picking up the tab for Mike, I feel in some ways entitled to weigh in and tell you this: you should thank God for Joe. You should be on your knees, hands prayerfully clasped with gratitude that he exists and is as generous as he is. You should be on the phone with him right now, telling him that you can't do the 9:30 appointment but you'll send your younger son, and that you'd like to help him sell the car, and he can keep the proceeds as your thank-you for the years of busting his butt in the service of your brother. Point out to him that selling the car now and gifting the proceeds is a heck of a lot smarter than selling it later and in-effect forcing that money to the nursing home as part of Mike's estate.
Just my $0.02.
P.S. If you impound that car, I think you'll put your son's job in some serious jeopardy. Tell your husband that you'll handle it next week, and cross your fingers.
P.P.S. Sell the stuff in the garage!!!