What are your thoughts of the names listed below for a sister to [name_f]Stella[/name_f]? Also feel free to add suggestions
[name_u]Celeste[/name_u]
[name_f]Colette[/name_f]
[name_f]Cora[/name_f]
[name_f]Gemma[/name_f]
[name_f]Greta[/name_f]
Lila/Lyla
[name_f]Lola[/name_f]
[name_f]Colette[/name_f] is perfect! Not too close in sound or meaning, like [name_f]Lola[/name_f] or [name_u]Celeste[/name_u] might be, but perfect in terms of style. Both have a kind of steely retro pizzazz that the pairing really highlights 
I really like [name_f]Greta[/name_f] too! Similar vibe…
[name_f]Maxine[/name_f]
[name_u]Simone[/name_u]
[name_u]Esme[/name_u]
[name_f]Gloria[/name_f]
[name_f]Cecile[/name_f]
[name_f]Inez[/name_f]
[name_f]Zita[/name_f]
[name_f]Opal[/name_f]
[name_f]Ingrid[/name_f]
[name_f]Astrid[/name_f]
[name_f]Petra[/name_f]
[name_u]Vivian[/name_u]
[name_f]Goldie[/name_f]
[name_f]Olive[/name_f]
[name_f]Georgia[/name_f]
[name_u]Marian[/name_u]
[name_u]Louise[/name_u]
[name_f]Edie[/name_f]
[name_u]Jean[/name_u]
From your choices the best fit for a sibling would be [name_u]Celeste[/name_u] or [name_f]Gemma[/name_f].
[name_f]Stella[/name_f] has that warm, vintage, spunky feeling with the sparkles of the stars!
A few other nice fits would be:
[name_f]Estee[/name_f]
[name_f]Lucy[/name_f]
[name_f]Francine[/name_f]
[name_f]Aurora[/name_f]
[name_f]Juliette[/name_f]
[name_f]Louisa[/name_f]
[name_f]Selena[/name_f]
[name_f]Phoebe[/name_f]
[name_f]Larissa[/name_f]
[name_f]Carina[/name_f]
Best Wishes to you and your little one! 
I always thought [name_f]Stella[/name_f] & [name_f]Leonora[/name_f] were nice!
[name_f]Stella[/name_f] & [name_f]Greta[/name_f] or [name_f]Stella[/name_f] & [name_f]Lola[/name_f] would be my picks.
Other Ideas:
[name_f]Stella[/name_f] & [name_f]Nina[/name_f]
[name_f]Stella[/name_f] & [name_f]Orla[/name_f]
[name_f]Stella[/name_f] & [name_f]Ada[/name_f]
[name_f]Stella[/name_f] & [name_f]Grace[/name_f]
[name_f]Stella[/name_f] & [name_f]Flora[/name_f]
[name_f]Stella[/name_f] & [name_f]Renee[/name_f]
[name_f]Stella[/name_f] & [name_f]Lucy[/name_f]
[name_f]Stella[/name_f] & [name_f]Louisa[/name_f]
[name_f]Stella[/name_f] & [name_f]Molly[/name_f]
[name_f]Stella[/name_f] & [name_f]Rose[/name_f]
I think they’re all excellent options. [name_u]Celeste[/name_u] is a little theme-y with [name_f]Stella[/name_f], but if that’s your thing, it works.
Other ideas:
[name_f]Amara[/name_f]
[name_f]Anya[/name_f]
[name_f]Ayla[/name_f]
[name_f]Brynn[/name_f]
[name_f]Carly[/name_f]
[name_f]Cassandra[/name_f]
[name_f]Claire[/name_f]
[name_f]Corrina[/name_f]
[name_f]Karla[/name_f]
[name_f]Leila[/name_f]
[name_f]Mya[/name_f]
[name_f]Nora[/name_f]
[name_f]Olivia[/name_f]
[name_f]Rosalie[/name_f]
[name_f]Stephanie[/name_f]
[name_f]Sylvia[/name_f]
[name_f]Vera[/name_f]
[name_u]Vivian[/name_u]
[name_f]Aurora[/name_f]
[name_f]Esther[/name_f]
[name_f]Eliza[/name_f]
[name_f]Alice[/name_f]
[name_f]Grace[/name_f]
[name_f]Clara[/name_f]
[name_f]Amelia[/name_f]
[name_f]Eloise[/name_f]
[name_f]Adelaide[/name_f]
[name_u]Hazel[/name_u]
[name_f]Scarlett[/name_f]
[name_f]Delilah[/name_f]
[name_f]Daphne[/name_f]
[name_u]Willow[/name_u]
[name_f]Luna[/name_f]
[name_f]Nora[/name_f]
[name_f]Athena[/name_f]
[name_f]Anastasia[/name_f]
[name_f]Ophelia[/name_f]
[name_u]Ivy[/name_u]
[name_f]Violet[/name_f]
[name_f]Astrid[/name_f]
[name_f]Mabel[/name_f]
[name_f]Beatrix[/name_f]
[name_f]Helena[/name_f]
[name_f]Charlotte[/name_f]
[name_f]Elizabeth[/name_f]
With Stella, I like Cora, Colette and Lola. Cora has a similar modern yet vintage sound and a sharpness so the names don’t blend. Colette is sharp but sweet and stylish and Lola is fresh and sweet - they match without sounding too similar
Based on yours and with sister Stella, I’d suggest:
Flora
Ruby
Isobel
Josie
Cleo
Nadia
Anya
Freya
Edie
Kaia
Juliet
Jasmine
Phoebe
Amelie
Daisy
I see [name_f]Stella[/name_f] as a 1940’s working girl, a secretary with chutzpah.
[name_f]Stella[/name_f] and [name_f]Brenda[/name_f]
[name_f]Stella[/name_f] and [name_f]Norma[/name_f]
[name_f]Stella[/name_f] and [name_f]Trixie[/name_f]
[name_f]Stella[/name_f] and [name_f]Trudie[/name_f]
[name_f]Stella[/name_f] and [name_f]Libby[/name_f]
[name_f]Stella[/name_f] and …
I love [name_f]Greta[/name_f]! I think it’s such an underloved name. And it sounds so sweet with [name_f]Stella[/name_f] with the 2 syllables and matching -a ending but not too matchy that it becomes cheesy. [name_f]My[/name_f] second choice would be [name_f]Lola[/name_f] although “Stella and Lola” might get tongue twistery. I also like [name_u]Celeste[/name_u] but with [name_f]Stella[/name_f] it might be a little too on the nose.
[name_u]Celeste[/name_u]!
Names with a similar meaning:
[name_f]Danica[/name_f]
[name_f]Elanor[/name_f]
[name_u]Seren[/name_u]
Setareh/Sitara
[name_f]Tara[/name_f]
[name_f]Twila[/name_f]
[name_f]Luna[/name_f]
[name_u]Nova[/name_u]
[name_f]Aura[/name_f]
[name_u]Evren[/name_u]
[name_f]Hala[/name_f]
[name_f]Selene[/name_f]
[name_f]Aurora[/name_f]
[name_f]Sunniva[/name_f]
[name_f]Araceli[/name_f]
[name_f]Elara[/name_f]
Iah
[name_f]Lyra[/name_f]
From your list, I really like [name_f]Stella[/name_f] and …Gemma or [name_f]Cora[/name_f]. [name_f]Lola[/name_f] is super sweet also.
I really want to like [name_u]Celeste[/name_u], but I can’t get over it sounding like molest. 
A few suggestions in case you like anything:
[name_f]Julia[/name_f]
[name_f]Lydia[/name_f]
[name_f]Clara[/name_f]
[name_f]Eloise[/name_f]
[name_f]Eve[/name_f] or [name_f]Eva[/name_f]
[name_f]Tessa[/name_f]
[name_f]Marina[/name_f]
[name_f]Juliet[/name_f]
[name_f]Lucia[/name_f]
[name_f]Lucy[/name_f]
[name_f]Natalia[/name_f]
I like [name_f]Colette[/name_f], [name_f]Greta[/name_f], and [name_f]Lila[/name_f] best
Unfortunately Celeste, Lola, and Lila/Lyla are a little too similar in sound to Stella for me although they are wonderful choices in their own right.
Cora gets my pick for favourite sister option, followed by Gemma! Love your list 
[name_f]Stella[/name_f] and [name_f]Colette[/name_f]
[name_f]Stella[/name_f] and [name_f]Adeline[/name_f]
[name_f]Stella[/name_f] and [name_f]Elodie[/name_f]
[name_f]Stella[/name_f] and [name_f]Faye[/name_f]
[name_f]Stella[/name_f] and [name_f]Clara[/name_f]
[name_f]Stella[/name_f] and [name_f]Lydia[/name_f]
[name_f]Stella[/name_f] and [name_f]Felicity[/name_f]
[name_f]Stella[/name_f] and [name_u]Eden[/name_u]
[name_f]Stella[/name_f] and [name_f]Paige[/name_f]
[name_f]Stella[/name_f] and [name_u]Sloane[/name_u]
[name_f]Stella[/name_f] and [name_f]Maren[/name_f]
[name_f]Stella[/name_f] and [name_f]Harriet[/name_f]
[name_f]Stella[/name_f] and [name_f]Maisie[/name_f]
[name_f]Stella[/name_f] and [name_f]Sylvie[/name_f]
[name_f]Stella[/name_f] and [name_f]Ingrid[/name_f]
[name_f]Stella[/name_f] and [name_f]Freya[/name_f]
[name_f]Stella[/name_f] and [name_f]Ruth[/name_f]
[name_f]Stella[/name_f] and [name_u]Esme[/name_u]
[name_f]Stella[/name_f] and [name_u]Darcy[/name_u]
[name_f]Stella[/name_f] and [name_f]Astrid[/name_f]
[name_f]Stella[/name_f] and [name_u]June[/name_u]
[name_f]Stella[/name_f] and [name_f]Daphne[/name_f]
[name_f]Stella[/name_f] and [name_u]Ruby[/name_u]
[name_f]Stella[/name_f] and [name_f]Georgia[/name_f]
All of them fit nicely with [name_f]Stella[/name_f], but I think [name_f]Colette[/name_f], [name_f]Lola[/name_f] & [name_f]Greta[/name_f] work the best. Some more suggestions:
[name_f]Charlotte[/name_f]
[name_u]Hazel[/name_u]
[name_f]Scarlett[/name_f]
[name_f]Clara[/name_f]
[name_f]Eloise[/name_f]
[name_f]Athena[/name_f]
[name_f]Daphne[/name_f]
[name_f]Delphine[/name_f]
[name_f]Astrid[/name_f]
[name_u]Artemis[/name_u]
[name_f]Felicity[/name_f]
[name_f]Calliope[/name_f]
[name_u]Blythe[/name_u]
[name_f]Cecilia[/name_f]
[name_f]Cosette[/name_f]
[name_f]Elodie[/name_f]
[name_f]Genevieve[/name_f]
[name_f]Eleanor[/name_f]
[name_f]Iris[/name_f]
[name_f]Agnes[/name_f]
[name_u]Florence[/name_u]
[name_u]June[/name_u]
[name_f]Frida[/name_f]
[name_f]Harriet[/name_f]
[name_f]Ida[/name_f]
[name_f]Enid[/name_f]
[name_f]Winifred[/name_f]
[name_f]Heidi[/name_f]
[name_f]Flora[/name_f]
[name_f]Lily[/name_f]
[name_u]Ivy[/name_u]
[name_f]Violet[/name_f]
[name_f]Rose[/name_f]
[name_u]Rory[/name_u]
[name_f]Daisy[/name_f]
[name_u]Harlow[/name_u]
[name_f]Clover[/name_f]
[name_f]Ava[/name_f]
[name_f]Clementine[/name_f]
[name_f]Maisie[/name_f]
[name_f]Mabel[/name_f]
[name_f]Poppy[/name_f]
[name_f]Josephine[/name_f]
[name_f]Ingrid[/name_f]