Charlotte to me has two themes: one is homespun American (Charlotte's Web or Charlotte, North Carolina) and the other is old-fashioned and proper (Charlotte Bronte or Charlotte Sometimes).  I tried to match both these styles.

boys:

Cedric (Little Lord Fontleroy, Ivanhoe)
Nathaniel (Hawthorne)
Fitz (not sure if this is your style but can be short for American Fitzgerald or Edwardian Fitzwilliam Darcy)
Austen (like Jane, but when paired with Charlotte might be too place-name-themey)
Dashiell (has that punchy nn, American Dashiell Hammett but has that old fashioned surname sound)
Byron (Lord Byron)
Beckett (Thomas a Beckett, Samuel Beckett)

and the American boys: Holden, Sawyer, Atticus and Finn.  All of these have a rascally, trendy sound which work well with Charlotte's popularity and farm girl sensibility, especially if she's a Charlie and not a Lottie.

girls:

Virginia (Woolf, also has that place theme and Elizabeth I association)
Evelyn (Waugh)
Josephine (Jo March, Empress Josephine)
Dorian (Gray)
Eleanor (Roosevelt, of Aquitaine)
Caroline (Charlotte is in North Carolina, mother of Laura Ingalls)
Eloise (Kay Thompson book character)

Let me know which are appealing to you and your husband so we can brainstorm some more.

Two that spring to my mind:

Tess 

Harper

Nice suggestions so far! I will second Nathaniel, Josephine, and add William, Anastasia, Sebastian, Samantha.

Oooh...so many excellent names fit your criteria! I'll have to restrain it to ten names for each :)

Boys: Oliver, Thomas, Arthur, Leo, Peter, Edward/Edmund, Henry, Lewis, Roland, Martin.

Girls: Catherine, Margaret, Mary/Marianne, Helen(a)/Eleanor, Anna/e, Jane/Jean/Joan, and Elizabeth all more or less fit your criteria, but it feels like they may not count. So with that in mind, perhaps: Alice, Frances, Clara, Harriet, Beatrice, Dorothy, Simone, Edith, Winifred, Florence/Flora?

Do you have any middle names that you're working with?

I can't hear Charlotte (Bronte) without thinking of Jane (Austen)-- two names that go together beautifully without screaming WRITERS (like Emily would with Charlotte).

I also like Edith (Wharton) and Willa (Cather) for you.

For boys: George, Henry, William, and Thomas

Not sure if these are repeats but here is what I found...

Boy

Atticus, Holden, Gatsby, Phineas, Aslan, Cash, Rhett, Oliver, Nicholas, Frederick, George, Edward, Henry

Girl

Jane, Lily, Josephine, Aurora, Lara, Audrey, Rosalind, Bianca, Juliet, Harriet, Lydia

Girls:

• Jane
• Harper
• Lyra
• Josephine "Jo"
• Scout
• Sylvia
• Maya
• Elinor
• Harriet
• Louisa

Boys:

• Jules
• George
• Henry
• Lewis
• Sawyer

 Edit: Coll's suggestions of Edith and Willa are lovely!

update: it's a boy!

I just looked up Charlotte Bronte on Wikipedia. She wrote some things under some pen names so maybe Currer Bell, Florian Wellesley, and Charles Albert could be transformed somehow. Also she was born in Thornton. Married an Arthur. Her father's name was Patrick. Or is all of this just TOO much? If you just want another poet in the same time period you could look at this website for inspiration:

http://famouspoetsandpoems.com/born/6/19th_century_poets.html

I like Blake as and option personally.

For a brother to go with sister Charlotte: Oliver, Arthur, Sebastian, Sawyer, Thomas, Jasper, Marcus, Dashiell, Edward.

Are there any names you are currently considering? or names you considered when your were expecting Charlotte?