Is it possible to challenge a gift deed done by my grandmother?

My Grand father died intestate 25 years ago. My grandpa had purchased a land 35 years ago and built a house in that land back then, but registered it in my Grandmother's name. The source of income to purchase the land and build the house was entirely borne by my Grandfather. They had 3 sons and a daughter. My father was the youngest and I'm the only child to my father. My father expired last month leaving behind my mother and me. Six months ago, My Grandmother had gifted that land with building to her eldest son. Looks like the gift deed was registered. This was not let to the notice of her two other sons and her daughter. (Back then my father was alive, when the gift deed was completed by my grand mother). The gift deed done by my grandmother was found out just a couple of days back. Kindly let me know if my paternal uncle(2nd son of my grandmother), aunt and I could challenge the gift deed done by my grandmother? Also let me know if a gift deed can be executed on a property, if the source of income to get the property was not from the owner of that property. Thanks in advance.