Relinquishment Deed

Dear Sirs, My Mother in law had an ancestral property in Goa which consists of a house and second one is a vast agricultural land where in she and her brother were the heirs. Her brother and his wife along with their 3children now adults(married) are still residing in the house. My husband was told by his cousin that they wanted the house on their fathers name and would require our signatures and by doing so we would get my mother in laws share in the agricultural land and hence proceeded to take our signatures without paying us anything for the house when they took our signatures they didn’t say they were doing a Relinquishment Deed of the agricultural land with the house in December 2017 the relinquishment was done. On 26th February 2021 I got two mutation notices in all our names one for the house and the second for the land. How can challenge this as I have been cheated even after being kind towards them and my Mother in law was diagnosed of Cancer in 2018 and they didn’t even offer us any financial help and we really need the land. Please help