I like [name_m]Helo[/name_m] for a boy and either [name_f]Aruna[/name_f] or [name_f]Lenya[/name_f] for a girl!
A few other suggestions (I’ll mostly suggest two syllables as you seem to like those!)
Brothers: [name_m]Whittaker[/name_m], [name_m]Tristan[/name_m], [name_m]Ivan[/name_m], [name_m]Drake[/name_m], [name_m]Oliver[/name_m], [name_m]Alwin[/name_m], [name_m]Thatcher[/name_m], [name_m]Thane[/name_m], [name_m]Lionel[/name_m], [name_m]Xavier[/name_m]
Sisters: [name_f]Isolde[/name_f], Nolwenn/Nolwynn, [name_f]Daphne[/name_f], [name_f]Mariah[/name_f], [name_f]Jane[/name_f], [name_f]Freya[/name_f], [name_f]Olwen[/name_f], [name_f]Prisca[/name_f]