Blackmail from my father's second wife

My father passed away 3 years back and mother 2 years back and are survived by 4 children. My father had a second wife - Mrs X (not sure if she has a proof of wedding though) but we knew that she lived with my father for the last 30 years or so and has 2 children from this relationship. While we are in posession of my father's ancenstral property, my father left the following for Mrs X. 1. A house in which Mrs. X sold for around 1 cr and purchased house in another city after my fathers death. 2. A plantation on rented plot in U.P. worth around 8 Lakhs, in our control at the moment. 3. A house in Noida worth 60 Lakhs which in currently in my name. 4. Some money, policies, properties that we are not aware of. Now Mrs. X has been demanding Rs 15 Lakhs for the plantation and the transfer of the house in Noida immediately else she is threatening with revealing personal details of my father, his affairs, scandals, etc. to our extended family and relatives and that she will come to our houses and create a reckus. While we dont have much problem giving her the house + Rs 6 Lakhs, what we are worried is that this blackmailing may continue in future. My questions. 1. What is it that she can legally claim from us with or without a proof of maraiage? 2. What should we do to ensure she does not blackmail us and\or malign the image of my father and family in future? 4. Should we talk to her and agree on a settlement or take the legal route?