Ancestral property dispute between heirs

My great grandfather had 2 separate properties on each side of the road. One of those property was inherited by my grandfather and other one was inherited by his (grandfather's) sibling. My grandfather has 2 sons i.e. my father and my uncle. But my father passed away in 2001 and my grandfather passed away 5 years back. So, in this scenario, is this property considered an ancestral property? Our family and my uncle's family used to stay under one roof but on different floors with separate kitchen. But I am an NRI now and no longer staying in the premises. This property was never partitioned or divided between any generations. My grandfather made a will (before dying) to give 100% of this property to my Uncle. So, in absence of my father, can I claim half of this property even though my grandfather made a Will? Is this WILL illegal as he has no rights to make a will as this is an ancestral property? Please clarify what options do I have and how can I claim my portion.