Query regarding the will and gift deeds

Hello Sir, Myself Bharath, working as a software engineer. This mail is with respect to a query regarding the will or a gift deed. We are a four member family, my father recently expired due some health reasons. Due to our job requirements me and my brother are staying in different geographic locations, and my mother stays at our home town (Andhra Pradesh). My mother is not agreeing or ready to stay with us. We have some father side ancestral property (agricultural land), which is transferred to my mothers name after my fathers death. Other than these, some agricultural land, house and residential plots are also there on her name (These properties are on her name alone, but earned by us and my father). Now due to some personal issues we are getting a sense that she is going to gift or will all the property to her own brother and brother's son. Is this legally possible as per Indian law. Do we have any right to go to court to challenge the will or gift deed. Please let me know any additional info. needed. Thanks, Bharath