I think I’d be tempted to break the pattern, unless you find a J name that is “just right”. I’d focus on letting it happen naturally rather than limiting/cornering yourself in 
[name_f][/name_f] Plus, since [name_f]Jubilee[/name_f] goes by [name_f]Billie[/name_f], it balances it out?
Of your options, I really like:
[name_f][/name_f][name_m]Josiah[/name_m] → strong but gentle, familiar and cool
[name_f][/name_f][name_m]Jairus[/name_m] → cool nickname [name_m]Jai[/name_m], strong and distinctive
[name_f][/name_f]Roniel → familiar but unexpected, gives you nn [name_f]Roni[/name_f].
[name_f][/name_f][name_m]Jedidiah[/name_m] → cool and clunky at the same time [name_f][/name_f]- nicknames [name_m]Jed[/name_m], [name_m]Jai[/name_m], and [name_f]Jez[/name_f] are nice nicknames
[name_f][/name_f][name_f]Elora[/name_f] → bright and pretty
[name_f][/name_f][name_m]Journey[/name_m] → playful and charming
[name_f][/name_f]If I were to name a sib to [name_m]Judah[/name_m] and [name_f]Jubilee[/name_f] “Billie”…
[name_f][/name_f][name_f]Keziah[/name_f] (Kai, [name_f]Kezzie[/name_f], Kizzy)
[name_f][/name_f][name_m]Jasper[/name_m]
[name_f][/name_f][name_f]Keturah[/name_f] (Tru, Kezzie)
[name_f][/name_f][name_m]Elionai[/name_m] (Eli, [name_m]Lio[/name_m], Nai)
[name_f][/name_f][name_f]Genesis[/name_f] (Ness, [name_f]Ginny[/name_f], [name_f]Gigi[/name_f], Issy)
[name_f][/name_f][name_m]Benaiah[/name_m] (Benny)
[name_f][/name_f][name_m]Zebediah[/name_m] (Zeb, Zai)
[name_f][/name_f][name_m]Josiel[/name_m] (Joss)
[name_f][/name_f][name_f]Azaria[/name_f] (Ari, [name_f]Aria[/name_f], [name_f]Zara[/name_f], Zazie)