Under Pennsylvania intestate law, when a person dies without a will, and they have no surviving spouse, the estate would go to his/her children. If there are no children, then the estate would pass to his/her parents. When a person gets divorced, generally, the ex spouse is not entitled to receive an inheritance. Without more information, it appears that the paternal grandparents have no right to their son's estate because he has children. If you would like to discuss this further, please contact my firm at 484-681-9710.