Ok. Your situation is complicated, and I'd be remiss if I didn't recommend you talk to an attorney.
That said...
Here's what the statutes say about GP visitation:
Missouri Revised Statutes 452.402 and 452.403 address the rights of grandparents to access/visitation. There is a presumption that the parents of the grandchild, legally married and living together with the grandchild, know what is the best interest of their child. The Court may, however, grant reasonable access/visitation when access has been unreasonably denied for more than 90 days and 1) the grandchild is the child of their deceased child; or 2) the grandchild's parents have filed for dissolution of their marriage; or 3) the grandchild resided in grandparent's home for a least 6 of the past 24 months. Visitation may only be ordered when the court finds it is in the best interests of the child. The right of grandparent access terminates upon the adoption of the grandchild.
If none of those apply, the case should be dismissed.
Regarding relocation, per MO statutes, the CP is ONLY obligated to notify the NCP and ANY OTHER PERSON WHO CURRENTLY HAS CUSTODY/VISITATION RIGHTS. If the GPs don't CURRENTLY have custody or visitation, then there's no obligation to inform them.
The GPs cannot, on behalf of their son, file anything.