Want to know the legal procedure to transfer the propert rights.

We are residing in a Pagdi system house in Mumbai, and it is in the name of my mother’s father (i.e. my grandfather’s name is there on the rent receipt) till date. My grandfather passed away in the year 1993, subsequently my grandmother passed away in the year 2000. Since 1958 my mother has been residing in this house (i.e. since her birth). I am 24 now, and my elder brother is 27, we too were born and brought up in the same house and we have all documents—Passport, Birth Certificate, Ration Card, Aadhar Card, Schooling, College Certificates etc...with the same address. My mother has siblings but all of them reside outside Maharashtra and they have never come/stayed here till date, all documents related to this house --like Electric bill, Ration card, gas cylinder bill are in my mother’s name. My question is to whom does the property belong to? Is there a provision, act, or legal procedures that favour us to transfer the property rights in the name of my mother? Also whenever the building goes for a deal the new flat will be entitled to whom?