Mother in law driving me totally nuts what should I do????

This is about way more than the car isn't it. Why isn't your husband supporting you? Why is your mother in law living with you? If she's really in financial need and sponging off you, then she needs to fit in with your rules and your needs. Your house, your car, your rules. How many times did your parents say "when you are living under my roof, you will follow my rules." Now she needs to hear it. I would get your husband to help you make a plan to get her, and all your husbands siblings out of the house. Maybe they'll qualify for aid and housing somewhere, but if they stay with you, the whole situation will get so much worse. In the meantime, make her take a taxi. If she has a job, she must have an income to cover the cost of a taxi for a day.