Transfer of property as a gift deed by the GPA holder, is valid?

Here is my query on "transfer of property as a gift deed by the GPA holder, is valid or not". My father has bought a 400 yards land in 1984 and due to family compulsion and pressure, has given the GPA to his brother in the year 1991 for some part (i.e.155 yards) of the land.We are not sure what is written in GPA and its clauses. But in 1992, my uncle( i.e.My Father's brother) got married and has gifted the same land of 155 yards to his wife. Later, he has sold part of land to others in the name of his wife in 1995. Since, the land was not registered by my father to his brother, can he gift this land to his wife ? and in turn, can his wife sell that property to others as he has made a gift deed in her name? My Father does not even have a copy nor the document number of that GPA which is given to his brother in 1991 and now he is acting against my father as relations between us are gone really worst. We got to apply for the gift deed made on his wife's name formally in the SRO, and we could not find the GPA document registered number in the gift deed.Is it not mandatory to mention the GPA registered number in the gift deed ? and if not, are there any other modes of executing gift deed by not mentioning the GPA registered number. We are not able to ask sro for GPA copy without a valid document number. Please clarify my doubts by letting me know with further proceedings and I am really sorry to ask all questions in one query.