If the other parent with custody refuses to sign the holiday consent form, you can ask the court for substitute consent for the holiday.
In the Netherlands, this is done by means of Article 1:253a of the Dutch Civil Code, which article can be used for all kinds of disputes between custody parents about the children. The request must be dealt with by the court within six weeks. If you can’t wait that long, you can start summary proceedings.
You can also ask permission for more holidays at once. For all holidays in the next year for instance. Or for maybe a fixed schedule of holidays for the next couple of years.