There is a procedure that can be used to uncloud a title or mistake in the paperwork. Best to have an attorney look at the paperwork and get more details. Did the brother give anything to the effort, or pay anything that would allow him to claim some portion of ownership? You wrote that he's on the deed of trust - is his name on the deed itself?
Even if he's done everything, and paid for a portion of the home, your mother can always attempt to use adverse possession to regain full ownership, and force him to action or lose whatever claim he has. This really isn't that expensive of a process, but it is definitely something you need to have an attorney to work with you on.