Bank accounts with 2 different account holders

My husband is on his mothers bank account just in case something were to happen to her that he would be able to get the money. My husband had a lien for a car creditor for $6,000. They wiped out his mothers bank account justifying that his name was on the account. My question is can they do that? He never writes check or withdraws money from her account. She is mad as hell? - Is this your question? Add additional information