(watertight of course!!!) and it is not "theirs" anymore
I don't think that would work. Then they would stay at a luxury house owned by somebody else and you get the sort of press that Victoria & Daniel had when they borrowed a private jet and yacht for their honeymoon.
Anyway, as far as I know Lex & Max bought land in Argentina. They probably end up going there when they need the advantage of a Southern hemisphere season, and stay in their timeshare in Tuscany for the European season.