Any Lawyers here??

My brother about 7 years ago bought his first home with the help of my parents was able to give the downpayment and all the fees then my dad was taking care of paying the house every month while my brother was only paying the small bills. Long story short my brother started dating this girl and he CHANGED to a whole different person, he started being mean to my parents, & not respecting them. Like this girl completely changed my brother. My brother and his girlfriend were living in the same house with my parents for about a month but they were acting weird all the time ( like they were always in their room) and one night he told my parents that they were going out to dinner and never came back home, so they moved out without telling my parents anything and until this day he hasnt given a call nor he answers my parents calls, but we do now hes ok hes just acting dumb. My dad got sick and can no longer work so hes trying to get long term disability and see how much hes gonna be given to see if he can continue making the house payments but yesterday my mom told me a realtor went to see the house to put it on sale but the realtor thought the house was empty and my mom told her the whole thing how my brother doesnt wannna talk to them so she said my brother cant sale the house since is occupied, my question is my parents they dont have a contract or a anything written saying that my dad was paying the house for the past 7 yrs because they think if my brother sells the house hes not going to give them any money and my parents really dont want to move out since my dad is sick and don’t really have nowhere to go since my house is really small and im just helping them with what i can 😔