Legal ways to challenge a will in case of ancestral property

My paternal aunt(Bua) is handicapped and unmarried and stays with us, she has got 11 acres agriculture land on her name transferred by my father through family settlement when my grandfather was alive as he was not in a legally stable mental stage, so entire ancestral property was divided in 4 parts 6 acres to me, 6 acres to my elder brother , 6 acres to my father and 11 acres to my aunt, I stay in Ghaziabad and my brother stays in Meerut while father and aunt stay in native place along with a servant, in 2016 a will was registered by my aunt declaring me and my brother as equal beneficiaries but in November 2017 she changed the will and gave entire land to my nephew, seeing this as a injustice my father made a will in my favour so just wanted to check if my brother can challenge my father's will and in that case can I challenge my aunt's will