Sale of Pagri Flat

This is a Pagri flat in Mumbai which is in the name of my father since around 1960. Rent is being accepted by the landlord and rent receipt is being issued in my fathers name. My Father expired a few years ago and now my mother stays in the flat, she continues to pay the rent and is being accepted by the landlord. She wants to sell the flat and agreed to give 33% of the proceeds to the landlord. however the landlord refuses to allow her to sell the flat. He says that my mother can sell it only to him. My mother is willing but the landlord has offered a very low amount as compared to the prevailing rate. This person is not the original landlord. he purchased the building some years ago from the original landlord, and thereafter has back many flats in the building by giving very low amounts and moving tenants out. He has several flat in the building in his possession. Question: 1. Can the Landlord stop my mother from getting a buyer fro the flat even though she is prepared top pay 33 % of the sale proceeds to him? 2. Can the Landlord force my mother to sell the flat to him at the amount that he fixes. 3. How should my mother handle this situation. Thanks.