You either buy him out or file a partition action in court.

This is a Q&A forum. You have not asked a question. Call the police.

The "how" to file a lawsuit is by hiring a lawyer. Just like the "how" to do surgery is by getting a doctor.

Assuming you are active duty military go to the Trial Defense Service on base.

This is a Q&A forum. You can use the Find a Lawyer tab above.

Can you sue? Of course. Will you win? That is up to the judge. Can you collect if you do win? No way to know.

This is a Q&A forum. You have not asked a question.

No court is going to get involved in this family squabble unless you have some form of promissory note.

The only thing you can do is retain a local probate attorney.

You should speak to a local collections/consumer law attorney.