Good luck. Parents wishes always come first. Grandparents have few rights and i know of no situations in which grandparents were ever guven rights over parental wishes unless the parents had already been found unfit by the courts. In many states there is no such thing as grandparents rights. All rights belong to the parents and they can legally deny access to their children. You can sue in family court but i sure dont see that changing anyones mind.
"Grandparent" rights don't cost anything. As a Grandparent, you already have some, to a point, but instilling those rights through a court system would probably cost and you would need an attorney. It also varies from state to state. I assume you are speaking of visitation? There also is no guarantee you would be the winning party. The parent(s) have many more rights than the "Grandparent".