We 2 brothers and one sister made a relinquish deed in favour of our mother in absence of any will in 2016 after our father's death in 2015. My father had a will registered in 1999 with my sister and his friend as witness signatory. Now my mother is paralytic neck down and cannot speak or eat properly staying with our sister. We brothers were unaware of the will till recently. My sister got 50% of the property registered on her name without our knowledge and consent. Since mother cannot speak or write we cannot verify from her the facts. My fathers did not give any share to our sister and mother. As per the will my mother can enjoy the property till her last breath, she can neither sell or gift it to anyone. We brothers now want to revoke the RD. Kindly suggest us how to proceed.