[name_m]Lucien[/name_m] and [name_m]Gabriel[/name_m] sound really good together, distinct yet beautifully balanced. I personally feel like [name_m]Lucien[/name_m] and [name_m]Julien[/name_m] are a bit too similar in both sound and rhythm, which might cause some confusion as they grow up (especially when calling for one of them!).
[name_f][/name_f]Other names that could pair well with [name_m]Lucien[/name_m]:
[name_f][/name_f][name_m]Elias[/name_m]
[name_f][/name_f][name_m]Raphael[/name_m]
[name_f][/name_f][name_m]Matteo[/name_m]
[name_f][/name_f][name_m]Emil[/name_m] / [name_m]Elio[/name_m] / [name_m]Elliot[/name_m]
[name_f][/name_f][name_m]Sebastian[/name_m]
[name_f][/name_f][name_m]Maxim[/name_m]
[name_f][/name_f][name_m]August[/name_m]
[name_f]Hope[/name_f] this helps!