Gift Deed Cancellation - RoR Entry

The questions is related to land pertaining to XY12. My grandmother had 4 sons, I am the son of her 3rd son. My great-grandfather adopted my grandmother's eldest son because he did not have any male heirs. My grandfather did not have any lands so my great-grandfather made a gift deed in favour of my grandmother for a few of his survey numbers, which would be passed equally to her 3 sons apart from the adopted son. The rest of the property belonged to the eldest son. The land pertaining to survey no. XY12 was not in gift deed to my grandmother. After my great grand-father passed away, my grandmother and the 4 sons stayed as a combined family. During the 1970’s when the land ceiling act was passed, my grandmother and 4 sons distributed land verbally amongst each other with each getting equal share in land. XY12 was recorded in favour of my grandmother at this time. The ROR for XY1 initially had the name of the eldest son, which was struck off and my grandmother’s name entered in it’s place. Another survey no. which had my grandmother’s name was stuck off and the eldest son’s name was written it’s place. This was done to segregate lands according to the land ceiling act. Later in the 2000s when the passbooks were being issued. The land was again redistributed verbally amongst each of my grandmother, the eldest son and his wife, the other two sons. One of the son was excluded since he was mentally challenged. Here, the survey no.s mentioned in the earlier gift deed were now registered in favour of the eldest son and his wife, my grandmother still had XY12. Shortly around 2005 our family got split and my grandmother along with the younger 3 brother, including my father stayed together. In 2021, my grandmother registered XY12 in my name in form of gift deed. In 2022, the eldest son took my grandmother into his custody and issued a unilateral cancellation deed claiming that XY12 belonged to him since his name was struck off in the old ROR and there is not direct claim to the land for my grandmother (since it was not mentioned in gift deed provided by my great-grandfather). The eldest son got a letter signed by my grandmother revoking her ownership of the land and transferring it to himself. My grandmother is suffering from severe dementia hence he was able to take advantage of the condition. They then proceeded to cancel the gift deed and got the land registered in his favour. How do I proceed to contest this in civil court?