Validity of gift deed

Mr. A (owner of 2 story building) . Mr. B ( son of Mr. A) Mr. B got second floor from his father via registered sale deed 1999. Mr. B in 2012 told to his father to reconstruct the building via builder. Now Mr. B Execute Family GPA in Favour of his father( Mr. A) . and according to collaboration agreement Builder will make 4 floor out which 3 floor and 4 floor will retain by builder and 1 & 2 floor with 10 lac rupees builder will pay to Mr. A. and as per clause of collaboration agreement that he & his father will equal share holder of money and floor constructed by builder. In 2014 Mr. B made one sale agreement and in which he bought one floor from his father for Rs. 12 Lac ( Market value 70 Lac). In 2015 when Mr. A via gift deed transferred to other floor his daughter. Mr. B raised objection against gift deed & said as per GPO we both are equal share holder of both flats. out of which you sold your share via sale deed to me. now how can you transfer my property to other via gift deed. Now my question is what is the validity of Gift deed. and objection raised by Mr. B