I do see what you mean with [name_u]Elliot[/name_u] and [name_f]Elizabeth[/name_f] being close! I definitely don’t find them to close, as they’re different syllable counts and different feels! [name_f]Annabeth[/name_f], [name_f]Marybeth[/name_f], [name_f]Maybeth[/name_f], Rosebeth, or Amybeth might offer a good amount of difference. 
Also, I don’t really think [name_f]Charlotte[/name_f] it’s too common with your babes, but I totally understand if it feels to common to you! [name_f]Lottie[/name_f], [name_f]Lo[/name_f], [name_u]Arlo[/name_u], [name_f]Lotte[/name_f] (LOT-uh, as I understand the pronunciation), and [name_f]Carly[/name_f] are some other nickname choices!
And just for fun, some names that shorten to [name_f]Maddy[/name_f], [name_f]Aggie[/name_f], [name_f]Elle[/name_f] / [name_f]Ella[/name_f], and similar nicknames! I love that that’s the style you’re aiming for!! I really like a very “girly” feeling name myself.
[name_f]Rosemary[/name_f] nn [name_f]Rosy[/name_f], [name_u]Romy[/name_u], [name_f]Ro[/name_f], [name_f]May[/name_f], [name_f]Mary[/name_f], [name_f]Rose[/name_f]
[name_f]Agnes[/name_f] nn [name_f]Aggie[/name_f]
[name_f]Magdalen[/name_f] (maybe too close to Margaret?) nn [name_f]Maddy[/name_f]
[name_f]Eleanor[/name_f] nn [name_f]Ella[/name_f], [name_f]Elle[/name_f] (though this name and nickname are fairly close to [name_u]Elliot[/name_u], I think)
[name_f]Penelope[/name_f] nn [name_f]Ella[/name_f], [name_f]Elle[/name_f]
[name_f]Annabelle[/name_f], nn [name_f]Belle[/name_f], [name_f]Annie[/name_f], [name_f]Anna[/name_f], [name_f]Ella[/name_f], [name_f]Elle[/name_f]
[name_f]Noelle[/name_f], [name_f]Michelle[/name_f], [name_f]Gabrielle[/name_f], [name_f]Rochelle[/name_f] nn [name_f]Ella[/name_f], [name_f]Elle[/name_f]
[name_f]Rachel[/name_f] nn [name_f]Elle[/name_f]
[name_u]Hazel[/name_u] nn [name_f]Elle[/name_f]
[name_f]Matilda[/name_f] nn [name_u]Mattie[/name_u], [name_f]Maddy[/name_f]
[name_f]Amanda[/name_f] nn [name_f]Maddy[/name_f]
[name_f]Caroline[/name_f] nn [name_f]Carrie[/name_f], [name_f]Callie[/name_f], [name_f]Linny[/name_f]
[name_f]Alice[/name_f] nn [name_u]Allie[/name_u], [name_f]Lissy[/name_f]
[name_f]Adelaide[/name_f] nn [name_f]Laidey[/name_f], [name_f]Adele[/name_f], [name_f]Elle[/name_f], [name_f]Addy[/name_f] (I personally only one the ADD-uh-laid pronunciation, so I can’t imagine this name having any pronunciation troubles, myself!)
[name_f]Adele[/name_f] nn [name_f]Addy[/name_f], [name_f]Elle[/name_f]
[name_f]Adella[/name_f] nn [name_f]Addy[/name_f], [name_f]Elle[/name_f], [name_f]Ella[/name_f]
[name_f]Ada[/name_f] nn [name_f]Addy[/name_f]
[name_f]Elsinore[/name_f], [name_f]Elspeth[/name_f], [name_f]Lorelei[/name_f], [name_f]Rafaela[/name_f] nn [name_f]Elle[/name_f]
Best luck x