Every country has its own system of course. In the Netherlands the inheritance system is based on the principle that every heir gets a fair share. A Fideď Commis is not allowed since this is aimed to exclude heirs for the benefit of one (the oldest son, for an example).
Sweden also has no or very low succession taxes, while it is quite hefty in the Netherlands. The starting point in Sweden and the Netherlands will be the same: to ensure that the Bearer of the Crown has all properties at his/her disposal, deemed neccessary for the exercise of the royal function.
King Carl XVI Gustaf purchased jewels back from family members, maybe these were "lost" before the creation of the Bernadotte Foundation or were never part of this at all. It is a very intriguing topic. Our desire to see all grand collections to continue and to unfold their splendor vs the very personal considerations of private persons ("I prefer to see cash instead a diadem I can never wear").