Ah, you know, the ILs are in an awkward place. I know because my ex SIL used to call me after my brother dumped her in a MLC (she was actually his third wife, he didn't have a good track record). Frankly, he'd been treating her rudely for years and I kinda thought she was better off without him - your in-laws may feel the same.
As for your H stealing money from their account - all you can do is say you had no access, and you've discovered that he spent all your joint money too. Lob the ball back into his court.
BTW - do you think he could have a gambling or drug problem to account for the poor money management history? It's one thing to make poor decisions about saving with your joint money, but quite another thing to be spending his father's money that he has no right to.
