Old Cat, what is the legal ground for the ownership of those tow

Old cat, I am interested to know the legal ground for the ownership of those two Qing dynasty bronzes (rabbit and rat heads) claimed by their current owner?
By the same token, if the Japanese occupation of Diao Yu Island becomes a fact (actually it is now), does China or Taiwan lose its legal ground to claim it?
Your academic point of view may provide the Chinese government to act on disputed artifacts or disputed territories now.

This discussion should be restricted purely to academic purpose.