You should contact an attorney here in San Antonio to discuss your options based upon the specifics of your case. The ages of the children and the motivation of the grandparents may play a role in what action you can or cannot take.
They could file for grandparent visitation rights under certain circumstances--not sure they apply here. Family Code 153.432, and 153.433. But I think that they just want to use their son or daughter's visitation? Most custody orders gives the visitation parent the right to designate a competent adult to pick up and drop off the children. So if a stranger to you and the children can be designated, grandparents certainly can. Whether you want to file something to keep them from removing the children from the State is up to you. But couldn't you just talk about your concerns with them and let them get reacquainted with their grandkids gradually until you all get to know each other again. Sounds beneficial for the children to have extended family be involved in their lives. Is it not?
It's unclear from the question whether the grandparents are asking to visit or trying to obtain possession of/access to the child. If it's the latter, then a court can order access or possession by a grandparent if one of the biological or adoptive parents has not terminated rights, AND the grandparent(s) overcome the burden that the parent acts in the best interest of the child, AND one of the following is true: the child of the grandparent who is the parent of the child of the suit has been incarcerated for more than three months, has been found incompetent by a court, is dead, or does not have actual or court-ordered possession of the child.
It's unclear from what you've said whether the grandparents would meet this test, though it is important to note that the courts tend to give significant leeway to parents in making the decisions best for their children.
Your best bet is to contact an attorney in your area for a more in-depth consultation and examination of the facts of your case in light of the law.
This answer is based on the limited information provided and does not constitute legal advice or form an attorney-client relationship. For a more thorough evaluation of your case, please contact our offices to set up a consultation.
Read the order. Can the noncustodial parent appoint an adult to pick up and return the child?
For longer solution, consult with an attorney.
This answer DOES NOT establish an attorney-client relationship. This answer is based on the limited information provided and is not intended to be conclusive advice. There are likely other factors that might influence or change the advice after a more lengthy consultation.