This is quite a thread.
Word of advice to people who are dealing with something similar or whenever they do.
If you are in charge of a house and you have part ownership, and you have insane behavior from people. It is in your every interest to take action against anyone and everyone who is destroying your house. You are paying the mortgage and its your money getting sunk in.
If the insane person is not an owner, evict them immediately. The sheriff can serve the eviction easily. (In this case, I would have evicted the brother)
If the insane person is an owner, you need to gather as much evidence to get them institutionalized or in a care home (for those insane elderly relatives). If you can show police video evidence of any misdemeanors they commit or damaging the property, your case becomes stronger every time. Get police reports and as much video as possible. Build your case against them. You need to get acquainted with the authorities on a first name basis. Build a relationship there, get them on your side. Once they have lost their freedom or declared insane, you can move forward with your ownership issues. (I actually had my grandpa declared insane and was a danger to himself solely on video evidence of yelling at me drunk and falling down the stairs and injuring himself needing medical attention and unable to identify himself at the hospital)
This may seem like a complete no brainer, but lots of people never thought about leaving absolutely no accessible food to lunatics who are squatting in the house. Not a single bit of food, utensils, cups, or plates. It is unlikely they can acquire such basic things on their own. Don't make it easy to live there. (Had to do this with a deadbeat uncle who was leeching while I was dealing with grandpa)
Again, these situations are difficult to deal with, but you gotta come into them with a game plan, guys.
Good luck to the OP. I hope you find peace of mind soon.