Wonderful pictures. I think it is a mix of jewelry from the foundation and private bijoux. The sons of Princess Margriet have 4 grades of consanguinity with King Willem-Alexander. For the succession and the Royal House Act, they are too far related. They no longer belong to the Royal House and they are no longer successors to the throne.
They are not excluded to have the usufruct from the various foundations, when the King decides so: "To encourage that descendants of Her Majesty Queen Wilhelmina, Princess of Orange-Nassau have at their disposal the necessary or desired properties for the execution of the royal dignity. The Foundation is managed by the Bearer of the Crown. Reg. Nr. S.151.002." (Statutes of the Foundation Crown Properties of the House Orange-Nassau, established 1968).