Mother bought property through brother who is now not giving property

dear sir my mother purchased a small flat through my younger brother he uses her money but want to grab the flat by retaining the flat papers with him on repeated request he refused to return my mother is ailing age 79 years she is living with me in a rented aparment presently separately from younger my younger brother harrass her along with his wife when she lived with him in a flat purchased by my father he has estrange relation with all first family members plz advice how to take my mother flat papers from him legally we are muslim