Property from wife’s family

Dear Sir, My father is 80+ years old and I am his son from his second marriage. First my father married his elder sister Muniyammal’s only daughter Savithri in 1966 and his first wife Savithri died in 1973 due to health issues and there is no children from that marriage. Later my father married my mother in 1975 and have 3 children. Here the question is about legal property rights for my father from his first marriage as per below scenario 1) His father-in-law died when Savithri was a child. 2) His mother-in-law (Muniyammal) got 7.5 acres of land from her father-in-law through court order in 1961. 3) The land was managed by her and later in 1994 she wrote a ‘Will’ saying that property will go to in the name of her another brother’s sons after her demise and it was registered. 4) Later in 2010, she made a registered Sale deed in the name of her brother’s sons for selling property for 4.5 lakhs rupees for her expenses. 5) The Will registered in their name in 1994 was not cancelled till date. All these activities were happened without my father’s consent and knowledge. 6) Muniyammal died in 2016. Is there a way that my father can file a case now and get the property in full or part belongs to his deceased wife? Need your valuable legal advice on this matter. Thank you!