Gift deed

Very old Senior citizens Father & Mother made A registered gift deed of self earned property to only one son out of 4 children (2 sons & 2 daughters). After 2 years, father writes letters to sub registrar , Deputy Commissioner & District Magistrate asking them to cancel the Gift deed as it was done by force by his son by creating tension. Letter has reached officials & friends & relatives after his death. Mother is so scared of son & daughter in law that she is not willing to talk about it, especially now that her husband is no more. Possibly, son must have forced her to give consent letter to him or even take her blank signatures. He has usurped all the properties by means of gift deeds in his favour. Can this be challenged in court, civil or criminal or senior citizens forum. Assuming, mother is not going to give statement against the son or daughter-in-law, & May have signed blank letter, or letter saying she has done it voluntarily, can this case be fought & STAY order / injunction order be obtained against the Properties & Gift deed cancelled