I am confused.
You are in an upside down situation on your current home, owing more than it is worth, right now.
You are expressing concern about being homeless and how you do not want to live with your MIL.
You also said that you are "closing on a home, this month". I assumed this meant you were buying another house.
I am assuming your name is on the loan documents for the current house and you signed them. Have you read the documents? You can also call the lender and find out the details, for yourself. You will then know how much cash back he got and spent. Does it matter, at this point?
The foreclosure situation is indeed another matter and probably the least of your concerns at the moment.
You need an attorney to get a court order requiring him to pay child support. Such an order however, will not guarantee he will get or keep a job.
Maybe it will help the situation. Maybe not.
I feel so sad that you or anyone finds themselves in this situation.