Forged death certificate to cancel sale deed what can I do

a false death certificate of man has been made after 50 years of his death in rajasthan in 2014 by his son stating that his father was died in 1964. their main motive is to cancel sale deed which was made in 1968. but we got some evidence that his father was alive till 1979 and found another sale deed in another place in 1967 and thumb impression were got matched.. they have made false death certificate.. also death certificate has some mistakes also. two affidativits which were given were given by a man who was of 17 year in 1964 at that mans death . is affidavet given is valid?? any ruling?