Names that go with Jack and Alexandra?

[SomebodySaveMe]

Surname begins with a C. Alexandra is usually known by Lexie (unless she's in trouble) and I'm a bit stumped.
Any help would be brilliant.

Harry/Harriet?

My brother is called Harry. I quite like Harriet though with Hattie as a nn.

Olivia
Louisa
Ivy
Emma
Zara
Miranda
Hermione
Georgia
Susannah

Peter
Richard
William
Zachary
David
Edward
Benedict
Charles
Samuel

I have several on my list. Glad it's not just me that thinks they sound good together.

Arthur or Elliott for a boy
Cecilia or Claudia for a girl