Change of name of flat legally

I am living in Badlapur, Dist Thane, Maharashtra. My mother brought a flat in Badlapur in a CHS. It is registered in her name only. She died without making a will or appointing a nominee. My father and we 3 sisters (no brothers) being the legal heirs, we mutually decided to transfer the flat to my father's name which was done. Now my father died and appointed me as the 100% nominee and also made a will (on plain paper not registered but has 2 witnesses with no objections from my other 2 sisters. He has willed the flat to me only with complete rights to me to sell or use it as per my discretion and compensated my 2 sisters in cash. They have no objection to this. Can the society make me a member based on the nomination made by my father and his will? Do I become a legal owner based on my father's will and have the right to sell the property. If not what is the procedure to become a legal owner which will give me complete rights to either sell it or donate or gift it in future since I am a widow and have no children. I plan to make a registered will to take care of the property after me. Is that the correct way to do it. Please advise.