false will made how to get my property back

My name is mahendra singh yadav age 62.my father owned 10 acres of land and he died by cancer 13years back . But just before his death ,when he was in a state of unconsiousness by brother cleverly get a will signed by him transferring all my fathers property in the name of his own children but the man who was the witness in the will is ready to gave the statemant that my father was not in a condition to sign the will now what can i do to get my property back Please guide me about this Is their any chance of getting half of my father,s property