Can grandfather sell out ancestral property without consent of family?

We hava ancestral property of 7.5 acres agricultural land in one survey number. Out of this 7.5 acres, 2.5 acres were transferred by my grandmother (Fathers mother) to her daughter (Fathers sister) without informing to either my father or myself.My grandfather has expired in 1996. Does my grandfather has any right to transfer ancestral property without consent of my father or my self. I have checked the land records also, it reflects 5 acres of land registered in my name & another 2.5 acres in my Father's sister name I am 30 years old & belong to Hindu religion.