Do all legal heirs have rights in parents’ property?

A property was purchased after selling my grandfather’s property, but it was registered in my mother’s name jointly, with my mother as the first owner and my father as the second. Only their ration card number is mentioned in the 1989 documents. There are two electricity bills — one in my mother’s name and another in my father’s name — but the address on both doesn’t match the room details as per the Huntsman book. Do all legal heirs have rights over this property while both parents are alive? Can either parent, or both together, transfer the tenancy rights to someone else without the NOC of all legal heirs? One of the electricity meters has recently been changed from my mother’s name to the youngest son’s name jointly (with the son’s name appearing first). We recently discovered (after 3 years) that an unregistered gift deed exists for this, as the property is in a Mumbai slum.