My grandfather bought some land, and after he passed away, his two sons divided it. Now, my father wants to sell his share of the land without asking us. Can we prevent him from doing so?

Under Indian law, your father has the right to sell his share of the inherited land without your consent. You may have a claim if you can prove that the division was unfair or that your father is mentally incapacitated. However, preventing the sale solely based on familial ties is unlikely.