I would personally stay away from names with an s sound, so [name_m]Jude[/name_m] isn’t the only one left out. You have [name_m]Elias[/name_m], and [name_m]Issac[/name_m] which both have a prominent -s and [name_m]Felix[/name_m] which has the -ks, and then [name_m]Jude[/name_m] doesn’t have that. This would make me lean towards [name_f]Margot[/name_f], [name_f]Willa[/name_f], [name_f]Nina[/name_f], and [name_f]Thea[/name_f]. As long as one of the girls doesn’t have an -s, that works too!
[name_f][/name_f]Personally, I would go with…
[name_f][/name_f][name_f]Margot[/name_f] [name_f]Nina[/name_f] and [name_f]Sylvie[/name_f] [name_f]Thea[/name_f] 
[name_f][/name_f][name_m]Felix[/name_m], [name_m]Elias[/name_m], [name_m]Jude[/name_m], [name_m]Issac[/name_m], [name_f]Margot[/name_f], and [name_f]Sylvie[/name_f] 