I like
Charlotte Brewster an absurd amount. It's the perfect tomboy name.
Christina Margaret is also really nice - I especially love the use of
Kiki. I love fluffy nickname like this:
Kiki,
Mimi,
Gigi, Bibi,
Dodie, etc. There is something so relaxed-chic about them. I prefer
Kiki as a nickname for
Katharine myself, but I suppose
Christina works.
I also agree that
Elle is a bit "meh" compared to her sisters. She should have had a longer name, like
Kiki does.