How to get the share of property which was gifted for bank loan

My father gifted his share to his mother which he had got from our ancestral property ..he did this because my grandmother wanted loan to show the bank collateral property papers which she did not take afterwards ..so in a way she lied to my father ..she got the gift deed registered and later divided it into four portions from my Father's share ..is this gift deed valid ..where we were getting the entire property ..my grandmother did this n now we are entitled for 1/4th of the share ..what can we do to get back the original share that my father was entitled to ..as my grandmother cheated on him