How did he get that type of loan without your mother's consent? Did he forge her name to the application?

She needs to be working with a lawyer on that issue, unless you haven't told us something important such as the house being post-foreclosure.

If a plaintiff files a divorce case, he places his address on file with the court. I assume he doesn't have a lawyer as, if he did, you would simply serve his lawyer's office. If pleadings served upon him start to be returned because he has moved without updating his address, go to the court hearing with the sealed, returned documents and indicate to the court that you attempted to serve the plaintiff but he has vanished. Note that mom should be sure that she has a counterclaim for divorce filed - if she has already filed one, she can explore the possibility of seeking a default on the counterclaim. If she has not, she risks that his divorce case will be dismissed based upon his disappearance rather than continuing based upon her counter-complaint.