Congratulations on baby #5 

Your kiddos have such classic names! Looking at your list I think I would scratch off [name_u]Eden[/name_u]. I think [name_u]Eden[/name_u] just feels very different as a biblical place name the name feels modern and is unisex which feels different to your other kiddos.
This leaves [name_f]Gwendolyn[/name_f], [name_u]Hazel[/name_u], [name_f]Hannah[/name_f] & [name_f]Naomi[/name_f].
[name_f]Gwendolyn[/name_f] is very graceful, majestic and has a daring whimsical flair. I also like the nickname [name_f]Gwen[/name_f]. However she wouldn’t be my first pick for your siblings names she doesn’t feel that cohesive.
[name_u]Hazel[/name_u] is lovely and feels very cohesive with your kiddos she’s down to earth, laid back, outdoorsy and classic. [name_u]Hazel[/name_u] is beautiful and I like that she matches well with [name_f]Eloise[/name_f] as she’s not biblical.
[name_f]Hannah[/name_f] is a sweet friendly girl next door name she’s everyone’s best friend and has a nostalgic feel to her. I am a fan of [name_f]Hannah[/name_f] and she does feel very cohesive but she is as sparkly as your other options.
[name_f]Naomi[/name_f] is gorgeous, elegant and underused/underrated a truly gorgeous name and I love the nickname [name_f]Mimi[/name_f] for her. You could always use [name_f]Noemi[/name_f] to avoid those nicknames but still get a similar feel.
You’ve had lots of lovely suggestions so count any repeats as me being in agreement with the berries
[name_f]Eloise[/name_f], [name_u]Daniel[/name_u], [name_u]Benjamin[/name_u], [name_f]Lydia[/name_f] and…
[name_f]Flora[/name_f]
[name_f]Abigail[/name_f]
[name_f]Annabel[/name_f]
[name_f]Felicity[/name_f]
[name_f]Verity[/name_f]
[name_u]Fern[/name_u]
[name_f]Serena[/name_f]
[name_f]Violet[/name_f]
[name_f]Eve[/name_f]
[name_f]Miriam[/name_f]
[name_f]Colette[/name_f]
[name_f]Nina[/name_f]
[name_f]Gwyneth[/name_f] ~ feels more laid back and cohesive with your sibling set then [name_f]Gwendolyn[/name_f]
[name_f]Caroline[/name_f]
[name_u]Ruby[/name_u]
[name_f]Juliet[/name_f]
[name_f]Jemima[/name_f]
[name_f]Ruth[/name_f]
[name_f]Sarah[/name_f] (a lovely name that’s unheard off for young children/babies)
[name_f]Clara[/name_f]
[name_f]Jane[/name_f]
[name_f]Phoebe[/name_f]
[name_f]Kate[/name_f]
[name_f]Tess[/name_f]
[name_f]Nora[/name_f]
[name_f]Joanna[/name_f]
[name_f]Chloe[/name_f]
[name_f]Hope[/name_f]
[name_f]Hope[/name_f] this helps