Good luck with that Georg. How about we give those things back to the people your family stole them from or who unwilling paid for them with their tax dollars. That I can get behind.
Can the US also get behind the idea to give back all the stuff, that allied soldiers looted in the aftermath of the war(s)? None of that was ever required to be given back to the owners, even though a lot of those owners were jewish...
I don't think any of those Hohenzollern riches should go back into their private coffers. The Hohenzollern (and that goes for each and every royal family) were the monarchs of the german empire, the representatives of the country and as such the castles and the art, the jewels and all those treasures should belong to the country and should go into museums. If a gift was made by lets say the russian emperor or the chinese or the congolese people, than this gift wasn't meant for Fritz or Georg, but for the German Emporer. So it IMO wasn't personal, but symbolic...