With [name_m]Solomon[/name_m] and [name_f]Polly[/name_f], I like:
[name_m]Mack[/name_m] - this would make such a cool, eclectic set
[name_m]Jonah[/name_m] - shares that gentle feel
[name_m]Rocco[/name_m] - again, this adds something playful and cool -
[name_f]Ada[/name_f] - vintage and friendy
[name_f]Daphne[/name_f] - fits the clunky-but-stylish vibes of [name_m]Solomon[/name_m] and the sweetness of [name_f]Polly[/name_f]
[name_f]Martha[/name_f] ‘Mattie’ - love the idea of [name_f]Mattie[/name_f] with this set!
If I were to name a sibling:
[name_m]Solomon[/name_m], [name_f]Polly[/name_f], and…
[name_m]Casper[/name_m]
[name_m]Kip[/name_m]
[name_m]Cosmo[/name_m]
[name_m]Auden[/name_m]
[name_m]Ozias[/name_m]
[name_m]Rex[/name_m]
[name_m]Linus[/name_m]
[name_m]Inigo[/name_m]
[name_m]Bram[/name_m]
[name_m]Orson[/name_m]
[name_f]Nadia[/name_f]
[name_f]Thessaly[/name_f]
[name_f]Keziah[/name_f]
[name_f]Sarai[/name_f] (am I allowed to say this 
)
[name_f]Adele[/name_f]
[name_f]Cleo[/name_f]
[name_f]Jemima[/name_f]
[name_f]Abilene[/name_f] (Billie?)
[name_f]Anya[/name_f]