Gift deed creayee by Forgery and original owner is dead.

In 2017, My uncle cheated my Mother and her Sister by creating a gift deed in their absence. The flat was originally in my Granny's name, she was sick and she passed away in 2017. The property went into redevelopment in 2017. He took her thumb impression and created the gift deed and all the agreement with the builder in his name. Both sisters were unaware of it. I would like to know: 1) Can the gift deed be valid if it is created in the absence of other two children? 2) If I make video evidence and calling recordings of me and my uncle's conversation that he did everything without letting anyone know, how he cheated and so on, then would it be considered in court? 3) I had recorded a video where my granny had said that all three should share it (though not very clear as she was on bed during her last day) Any suggestions on how my mother and sister can get thier shares?