Legal rights on property distributed by parents

My father's property that inherited in the form of land and house. This propety my grandfather allocted to his 2 sons and now both of them  are no more. Unfotunately today my co-brother surpised me by asking his share saying that he did not think it was allocated properly. Is this logical or legallly admissible in the court as decades have passed and there were no issues until I listed the land for sale.