I pay a child support to my ex wife, our son has since moved in with his grandparents(her parents) should my order be reduced?

Details of why your child is not living with the mother, and is now living with her parents should be addressed. This is best down with an attorney directly that you may wish to retain. If the mother is not the one responsible for the child's care, then a modification may be in order. If not a change in the amount, a change in to whom the payments are made so you are certain that the funds are benefiting your child.

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DISCLAIMER: This answer is provided in response to a "hypothetical" question and provided for general, informational purposes and does not create an attorney/client relationship. The information presented is not legal advice and may change based additional information and research. It is recommended that you speak to an attorney to discuss your specific legal issues.