family dispute over duplex

I have a question over a family dispute. My Mother and Father co-own a two family duplex with my brother . My father and my Brother are both on the deed and the note. My brother made an agreement that my father sell his home and give him the money it was $50k. And for that my brother would let him and my mother live their till they died. My dad is 88 yrs old. Its twelve years later and my brother has now stopped paying the mortgage and wants my mom and dad out of the duplex. He has been late so many times it has ruined my dads credit. So they have no choice but to start paying the entire mortgage now. Which was not part of the deal. My father has nothing from the verbal agreement in writing but has many witnesses who has heard him say that he would pay the loan. My question is can my dad and mom keep the duplex by paying the mortgage and take my brothers name of the deed and note that he and my father are on? Or what can my parents do about this ?