Whenever money and family are involved just be prepared to never see the money again. His brother obviously has some issue that made him steal $6,000 from his own brother. And if you just let him slide you are an enabler for whatever issue he has and he will find a way to get more money from you. Never mind what it's going to do to his credit and the cost of getting rid of that, even if he doesn't call the cops and decides to wait it out until it drops.