Hi ReneeDawn. I see this was posted quite awhile ago but, on the off chance that this issue is still ongoing, I'll throw in my two cents. It sounds to me like perhaps your husband has a point. Your mom took advantage in this situation, and also took liberties that weren't hers to take by handing your car over to your uncle. And I think that no matter what happens someone is going to be hurt (either your mom or your husband, possibly your uncle, and definitely you). Your husband has every right to feel the way he feels, in my opinion. And you have no obligation to fix your mother's car. It's her car. It's one thing if she had been honest about that up front and just asked for it. But she didn't. And that's not your problem. It's also not your problem that your uncle was going through a difficult time...it's unfortunate, but not your fault. They acted without your consent.
What should you do? I don't know. But Your husband has offered three great suggestions.
Hope this helps. Again, just my opinion. Too bad there aren't more here to consider, but hopefully you've got it all straightened out by now. Good luck.