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You don't really get the custody case that he filed in PA dismissed; rather it is abated. This means that the PA court does nothing further on the custody case unless and until the NJ courts release jurisdiction. Motions to abate are rare so there is no set form. The closest example I could find is at this link.
For example, you could ask the PA court "to abate his custody case until such time that the PA court would have proper legal jurisdiction under Pennsylvania UCCJEA 23 Pa. Cons. Stat. Ann. § 5401 et seq." This is the text.