We have discussed the ownership of Princess Grace’s Van Cleef and Arpels diamond tiara here before, iirc. There is no proof that it now belongs to Princess Caroline. Caroline loaned it for her pre-wedding, but didn’t wear it afterwards. Instead, Princess Grace kept using the tiara after Caroline’s wedding. Also, the tiara was quite often included in exhibitions, and described as property of HSH Prince Albert. The same goes for the other jewels in the exhibitions; they were all attributed to the Prince. Personally I believe that Caroline holds the pearl drop and the fringe tiaras as loans, probably for life. Maybe she owns them, but the House decided to hide the actual ownership from the public (but why should they do so?)
The only thing I can say for sure, is that the jewellery policy of the Grimaldis is hard to understand.