I like [name_f]Charlotte[/name_f] best of your two. It makes for a beautiful, classic and literary sounding set. Also means they get their own starting letter and ending sound which is nice. [name_f]Ava[/name_f] is a tad too close to [name_f]Olivia[/name_f] and doesn’t have the same [name_f]English[/name_f], 19th storybook feel as the others. I love the nn [name_f]Lottie[/name_f] for [name_f]Charlotte[/name_f]. 
Other names:
[name_f][/name_f][name_f]Anne[/name_f]
[name_f][/name_f][name_f]Anna[/name_f]
[name_f][/name_f][name_f]Sophia[/name_f]
[name_f][/name_f][name_f]Lucy[/name_f] (not a big fan of but would match)
[name_f][/name_f][name_f]Mary[/name_f]
[name_f][/name_f][name_f]Frances[/name_f] “Franny”
[name_f][/name_f][name_f]Harriet[/name_f]
[name_f][/name_f][name_f]Marianne[/name_f] “Marnie”
[name_f][/name_f][name_f]Caroline[/name_f]
[name_f][/name_f][name_f]Margaret[/name_f]
[name_f][/name_f][name_f]Florence[/name_f]
[name_f][/name_f]Catherine/Katherine nn “Kitty”
[name_f][/name_f][name_f]Rosamund[/name_f] “Rosie”, “Romy”
[name_f][/name_f][name_f]Penelope[/name_f]
[name_f][/name_f][name_f]Audrey[/name_f]
[name_f][/name_f][name_f]Clara[/name_f]
[name_f][/name_f][name_f]Diana[/name_f]
[name_f][/name_f][name_f]Tabitha[/name_f]
[name_f][/name_f][name_f]Bronte[/name_f]