I think you should go for something a little mythical/ legendary and euro-fantasy sounding as the halfway point & to go with your other three.
[name_f][/name_f]I would suggest:
[name_f][/name_f][name_f]Seraphina[/name_f] [name_f][/name_f]- [name_f]Sera[/name_f], Raphie, Phina
[name_f][/name_f][name_f]Rosanna[/name_f] [name_f][/name_f]- [name_f]Rosie[/name_f], [name_f]Annie[/name_f]
[name_f][/name_f][name_f]Sylvia[/name_f] or even Anne-Sylvie (so pretty!)
[name_f][/name_f][name_f]Arabella[/name_f] [name_f][/name_f]- [name_f]Bella[/name_f]
[name_f][/name_f][name_f]Cosima[/name_f] [name_f][/name_f]- [name_f]Coco[/name_f], [name_f]Simmie[/name_f], [name_f]Mimi[/name_f]
[name_f][/name_f]Celestine/Celestina [name_f][/name_f]- [name_f]Esti[/name_f], [name_f]Stella[/name_f]
[name_f][/name_f][name_f]Aurelia[/name_f] [name_f][/name_f]- [name_f]Sunny[/name_f], [name_f]Raye[/name_f], [name_f]Lia[/name_f]
[name_f][/name_f][name_f]Ariadne[/name_f] [name_f][/name_f]- [name_m]Ari[/name_m], [name_f]Andie[/name_f], [name_f]Nina[/name_f]
[name_f][/name_f]Anna-Fleur / Mary-Fleur