Chalange registered will

My Father had made one will for his share in Agricultural land in Rajastha in favour of myself and also in favour of my mother in equal ratio and registered the same in 2011. We are three brothers and three sisters. My elder brother expired in 2009 but his wife and three adult childerns are living with same house. The mutation of land has been done in revinue records and conversion in residentail has been also done. We have ploted entire land in small polts of 100 sq.Mtrs and sold to builder.The property was self acquired by my father. Now my Bhabhi ( wife of my elder brother) is chalanging the will on ground of that my father were in depression at the time of writting will. Kindly suggest :- 1. Whether she can chalange on ground of mental fitness and how she prove that my father were in depression. How she can prove that my father were in depression at the time of writting / registeration of will. 2. property in now converted and mutation has been done in our favour, how & where she can chalange the will 3. Can she take stay on the sold property because builder is selling the plots and getting registered after sell of property through us. . 4. We are already agreed to give her 20% share in land and in case she chalange the will, she will get only 1/7 share. How we can reply in court that we are already agreed to give her 20% share and can court agree to accept our request or can we provide Bank Gurantee of 1/7 share till the finalization of case.. Kindly suggest,