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I can understand your frustration. You could file an emergency motion to enforce your divorce decree but it is unclear whether you could get this heard in time. I think judges like to see the parties work through these types of issues on their own. The unpaid child support and insurance are separate and you should seek to enforce those obligations. If the parents were to take the kids somehow you would have a criminal case for kidnapping against them.
If you have any additional questions just let me know otherwise a positive rating would be greatly appreciated.