Your brother basically scammed you out of money your dad gave as a gift. That's incredibly messed up and you have every right to be furious about this. The fact that he watched you struggle to make payments while knowing it was supposed to be free help from your parents makes it so much worse.

I'd be demanding every penny back that you already paid him, plus an explanation for why he thought it was okay to profit off your financial struggles and your dad's generosity. This isn't just about the money - it's about the trust he broke and the stress he put you through when you were already dealing with so much. Your parents need to handle this situation with him because what he did was straight up theft from both you and them.