Legal rights in mother's property

My father and my mother acquired/purchased a property by their joint efforts in 1968 in Ahmedabad. From the beginning, the property is registered on the name of my mother. My father expired in 2002 and my mother expired in 2017. My father had made a WILL (registered with 2 witness) in 1991 stating that "The property should be divided only between the daughters (my sisters) after his death. The son (me) and wife (my mother) shall not get any claim in the property after his death". My mother had made a WILL (notarized with 2 witness but not registered) in 2001 to give the property only to me after her death. Also my mother had made a last WILL (notarized with 2 witness but not registered) in 2016 to give the property only to me after her death. My questions are as below: 1. Is a will valid without registration? 2. If the property was registered on the name of my mother from beginning, can my father make a WILL for that property? Is such WILL valid legally? 3. Who has legal rights on this property now? 4. Can my sisters (all married) and their son/daughters claim anything in this property legally? 5. Is this considered as ancestral property or self-acquired property? Is Hindu Succession Act applicable on this property? 6. As my mother is expired now, what are the legal formalities to apply the WILL. Is probate required? 7. What all the documents shall be required if I want to sell the property in future? 8. Do I need to get sign from my sisters in NOC for selling this property?