Holy cow! He is completely irresponsible with money, but so many people are. It is not that he is simply getting on your nerves; his behavior is truly damaging your relationship, not to mention your financial life, which could put you out on the street. Some how he needs to figure out that you both can't possibly support his lazy brother. If you're moving anyway, it might be reason enough to move far away from the bum of a brother, although he could still call and beg/demand/lay guilt trips on your DH.
My sister's husband doesn't have any self control when it comes to money. When they married, she found out about all his unpaid debts and she took control of the finances and paid them off in about a year. He spends money on toys (action figures and such). She finally had to take away any checks and plastic money (debit/credit cards). I guess he complies, but doesn't appreciate it. However, he is irresponsible and would run around like an idiot and buy whatever he wanted, which would then cause checks to bounce when he did have access. He even did that when he was a soldier in Iraq. I'm not sure what he found to buy, but he bought it and left her in trouble back home. She gives him a small allowance, which he spends on snacks and such while working. I think he has childhood issues and tries to fill whatever was missing in his young life with toys now as an adult. It's pitiful; he had sheds full of toys, which he thought were an investment and collectible. However he's sure never made any money off them, other than returning them to the store in the original packaging.
Anyway, I love listening to Dave Ramsey on the radio here (3-5pm on AM stations). He is a financial guru, and has real, workable systems for people to get on track. Financial Peace University is an online class that you can take at your leisure. Maybe it would convince your husband of the seriousness of the issue. It's worth checking out. www.daveramsey.com Money matters are the number one cause of divorce, and second marriages are statistically more likely to fail than first ones. Best wishes to you!