Sorry to hear your H is being a pain about the house and money again. As far the threats go, I wouldn't advise worrying his mum by out and out telling her what he is threatening, but perhaps you can just say that you are concerned about him and he wouldn't tell you if there was anything wrong so would she perhaps keep an eye on him to make sure that he is okay.
Did you have a good relationship with your MIL before all this started? How do you feel about maintaining it? Just remember not to discuss the sitch with her. My MIL hasn't made any attempt to contact me or her grandson in months. I know she's been ill so I've not given it a second thought. We'll just have to see what happens at Christmas.
Both 50 S14 M 16 yrs (his 3rd; my 1st)
ILYBINILWY - 24 Dec 2012 H moved out - 27 Jun 2013 Legally separated - 6 Sep 2013 Closing the door and changing the locks