One Family, Multiple Houses

I like to do this and as the game doesn't support it directly, my workround is to keep a set of 'house sitter sims' on hand. Just pop one of those into the existing property, transfer whatever cash you want and move into the new house. You can the merge/split households to your hearts content using these house sitter sims. My celeb sim has a house in nearly every neighbourhood.

I have given em a uniform and made all the sitters as part of a club. Or just invite/visit them and ask to join household.