Settlement Of Divorce And Property

It's been more than 20 years since the divorce of my father and his first wife and son. The divorce was before the second marriage and divorce have been settled with all the assets acquired or inherited by my father during that time to be entitled to his first son. But now after my parents worked hard and acquired the properties and assests they are claiming it too. Is it legal to claim even after the settlement of divorce? Now that the properties are in name of my mother and sister do we have our rights to counter their demands as they had been settled with all assests acquired or inherited by father. Can I as a son and a brother gift my mother's acquired property and father's transferred property to sister. Without creating an opportunity to first wife and her son.