I believe the jewels are placed as an apart entity in the framework of the larger Foundation Crown Properties of the House Orange-Nassau. The goal: "Te bevorderen dat afstammelingen van H.M. Koningin Wilhelmina bij de uitoefening van de Koninklijke waardigheid de beschikking hebben over de daartoe nodige of gewenste roerende lichamelijke zaken." ("To promote that the descendants of H.M. Queen Wilhelmina, in the exercise of the royal dignity have access to therefore necessary or desired tangible properties.")
The King is custodian of the Foundation and decides but the sentence "the exercise of the royal dignity" seems to limit the core use of jewels to the Queen, the King's three daughters, the Princesses Beatrix and Margriet and finally the Duchess of Parma and the Princesses de Bourbon de Parme (who are descendants of Queen Wilhelmina and so now and then exercising the royal function).