Do grandparents have the right to seek visitation of grandchildren?
Unless your particular jurisdiction has statutory protection to that effect for the grandparents, then the answer to your basic question is “no.” To find out about your jurisdiction, consult with an attorney, or, alternatively, consult with the local office of child protective services. Beware, however, that the latter WILL often lie and stick their nose into places where it really doesn’t belong.
Unless it can be proven that the grandparents have abused the children, most courts will rule in their favor that they be given visitation. And if the grandparents are innocent, I marvel that selfish parents want to abuse their own children by denying them the love of their grandparents. What an awful world we live in today.