Father gave away property at fraction of value

Dear Sirs, Our father, who is 68 and suffered a stroke ten years ago, is susceptible to outside influences and displays erratic behavior, lack of judgement , extreme mistrust in his spouse and children. Under such a mental state, one of his younger brothers and his wife,who are known in the family for extracting money at various pretexts, convinced my father to secretly give away his inheritance (share of ancestral property) valued at at least 15 lakhs in 2010, for less than a lakh. This property was given by grandfather to both my parents as they helped finance two weddings and mother gave her wedding jewels. The deed was in fathers name only. Our mother and rest of us children had no clue about this till another relative told us about what had happened.We are, by God's grace well placed in India and abroad. Father lives in the house that belongs to my brother and earns a good pension that he spends on such schemes as he sees fit. We take care of our mother's living expenses as father is unwilling to spend a penny more than food expenses on her. Mother has protested a bit as she was hoping to keep that property for my sister's wedding expenses but none of us children have said anything. Our lifetime with father has taught us that it is of no use at all, he will do what he wishes to do. I wish to know if there is anything I can do for my mothers sake that she does not have to live in fear of losing the rest of our properties, most of which they purchased during their lifetime thanks to mothers frugal housekeeping.Many of these properties are under my fathers name. She keeps all the deeds and assets under lock and key and is under extreme stress as father threatens and abuses her for hiding away what belongs to him. Is there any legal recourse for us with respect to the sale of the property in 2010 and to ensure such an incident does not happen again ? Thank you Elder Daughter