I like [name_f]Lucy[/name_f] best from your list, but it does have a similar ending to [name_f]Sylvie[/name_f], so Iβd probably go with something different. Some possibilities:
[name_f]Maya[/name_f], [name_f]Sylvie[/name_f], and
I would choose [name_f]Elise[/name_f] for sure - matches nicely and means all three get different endings (if all three have two syllables, good if all different endings).
([name_f]Noa[/name_f] is going to date terribly, Iβd say, whereas your other two have staying power! And [name_u]Bryn[/name_u] is just that bit too stark and boyish compared to the other two. Sheβd complain about that!).
I think [name_f]Elise[/name_f] works beautifully with the sister set and is a great name in its own right. Stylistically, it has the contemporary feel of [name_f]Maya[/name_f] and the cosmopolitan feel of [name_f]Sylvie[/name_f], but it also has a distinctive ending.
[name_f]Lucy[/name_f] sounds lovely with the sibset but does share the ending with [name_f]Sylvie[/name_f] as the others have pointed out. [name_f]Elise[/name_f] is also a great name that gives each name its own ending and also fits really well