Huh? You say the BC doesn't matter. You cite an example using a court ordered visitation as proof that parents named on the BC are not exclusively entitled to see the children. Then you say courts can order that fathers be denied contact with their kids. Then you wipe it all out and say there are no court orders in this case. When there is no court order the only thing that does matter is the birth certificate.
You are almost there and if we were talking about this taking place at the mall or the movie theater you would be correct. The only thing that you are leaving out is the fact that the children were in the care of the grandfather and located on HIS property. Absent a court order to hand the children over, it is his DUTY to keep the children safely on his property.