Inheritance of great grandfather property

My mother's grandfather had a certain property which was evenly distributed to his 3 children. My maternal grandfather received a fair share and died without making any will against the property. Now my uncle has made a fraud will of my Maternal grandfather claiming that my grandmother,grandfather and the two uncle holds the right to the property absconding the two daughters. This will was presented before the court after 12 years of my maternal grandfather's death. How can my mother claim an equal share in the property? Kindly help