My elder sister is a member of a Housing Co-operative society in Rajarhat-Newtown, Kolkata. She has made my younger son as her nominee. My son is not yet earning anything. Can my sister in her own handwriting make a will giving the flat to my son ? My sister has a son, daughter-in-law and two grandsons. What should we do to get the possession of the flat after the demise of my sister ? Please advise.