I could be wrong but you needed to bring that up at the FIRST hearing in SC. SC should of been told that they did not have juristiction to take the case as the children were not residents for more than the 6 months. However if she filed when DSS took them, then maybe since NC had an open case could of needed a placement for the children. Since you already allowed the court to start I dont think you can stop them at this point.
Is the DSS case closed? If it is, then the grandparents would have a hard case to win against you. They would need to prove neglect to take children away. Maybe after DSS closed the case, the grandparents were told they would not win and that is why they are not paying the Law Gurdian? They may however get visitation rights?
You may be able to ask that the case be dismissed as the DSS case is closed and there is no abuse in the home. Do you or the grandparents have lawyers?