Having a baby girl- due in 1 week and seriously stressing.
If this baby was a boy we would have named him [name_m]Lachlan[/name_m].
Big brother is [name_u]Nolan[/name_u], and we were settled with the name [name_f]Isla[/name_f] but I just realized how popular is has become and am not as happy with it.
Other names we have considered but don’t love:
-Alana
-Gemma
-Elowen
-Anja
-Waverly
Middle name will be [name_f]Claire[/name_f] or [name_f]Clara[/name_f]
Iris?! Not as popular as Isla!
I really like Anja from your list, but I understand the need for something new & fresh! Maybe:
Astrid
Auburn
Aviva
Belle
Beatrix
Callie
Celeste
Colette
Cleo
Delaney
Daisy
Ever
Esme
Frankie
Flora
Felicity
Harley
Helena
Indie
Iris
Juliet
Kaia
Louisa
Lena
Lara
Lola
Louella
Liv
Margot
Maeve
Maisie
Marlowe
Maren
Mallory
Nell
Olive
Phoebe
Pippa
Sylvie
Tessa
Thea
Valentine
Vera
Winter
I love your taste in names - [name_u]Nolan[/name_u], [name_m]Lochlan[/name_m] and [name_f]Isla[/name_f] are some of my very favourites! I am always enthusiastic about [name_f]Isla[/name_f], even though I have known many little Isla’s, because it keeps that sunny-island-holiday vibe for me, no matter how much I hear it! If the popularity is a deal breaker for you though, here are some ideas based on [name_f]Isla[/name_f] and other names you’ve considered:
[name_f]Isola[/name_f]
[name_f]Iona[/name_f]
[name_f]Alara[/name_f] (meaning water fairy 
)
[name_f]Alaia[/name_f]
[name_f]Jemima[/name_f]
[name_f]Elodie[/name_f]
[name_u]Lennon[/name_u]
[name_f]Leni[/name_f]
[name_f]Avia[/name_f]
[name_f]Luella[/name_f]
[name_f]Elvie[/name_f]
[name_u]Alva[/name_u]
[name_f]Suvi[/name_f]
[name_f]Lowenna[/name_f]
(P.s. I do love [name_f]Isla[/name_f] Claire.)
I’ve never met an [name_f]Isla[/name_f], and I don’t think it’s too popular. Here are some other similar options (though I really do love Isla)
[name_f]Ayla[/name_f]
[name_f]Lila[/name_f]
[name_f]Orella[/name_f]
[name_f]Layla[/name_f]
[name_f]Ida[/name_f]
[name_f]Iva[/name_f]
[name_f]Lera[/name_f]
[name_f]Lara[/name_f]
[name_f]Oona[/name_f]
[name_u]Alma[/name_u]
[name_f]Inara[/name_f]
[name_f]Adara[/name_f]
[name_f]Kira[/name_f]
[name_f]Selah[/name_f]
[name_f]Vita[/name_f]
[name_f]Saskia[/name_f]
I love love love [name_u]Waverly[/name_u] [name_f]Claire[/name_f]! [name_f]Gemma[/name_f] [name_u]Clare[/name_u] would be my second choice.
[name_m]Hi[/name_m] there.
Ooh, I love [name_u]Nolan[/name_u]! [name_m]Lachlan[/name_m] would be amazing for a brother if you ever decide to have a third. 
I think that [name_f]Isla[/name_f] is beautiful and perfect with [name_u]Nolan[/name_u], but I do hear it constantly used in real life. People have caught on to how lovely it is.
Sorry for any repeats, but how about…
Aine-basically said like [name_f]Anja[/name_f] (more like Own-yuh, but I think Ahn-yuh works too), but spelled the Irish way.
[name_f]Alice[/name_f]
[name_f]Audrey[/name_f]
[name_f]Bridget[/name_f]
[name_f]Celia[/name_f]
[name_f]Cecily[/name_f]
[name_f]Delia[/name_f]
[name_u]Esme[/name_u]
[name_f]Eloise[/name_f]
[name_f]Flora[/name_f]
[name_f]Greta[/name_f]
[name_f]Lucy[/name_f]
[name_f]Louisa[/name_f]
[name_f]Lydia[/name_f]
[name_f]Maeve[/name_f]
Maire/Mara
[name_f]Maren[/name_f]
[name_f]Niamh[/name_f]
[name_f]Olive[/name_f]
[name_f]Phoebe[/name_f]
[name_f]Rose[/name_f]
[name_f]Stella[/name_f]
[name_f]Sadie[/name_f]
[name_f]Tess[/name_f]
[name_f]Tessa[/name_f]
[name_f]Violet[/name_f]
[name_f]Zella[/name_f]
[name_f]Hope[/name_f] this helps. 
[name_f]Frances[/name_f] “Francie” with either middle name-- this immediately came to mind because of the main character [name_f]Francie[/name_f] [name_u]Nolan[/name_u] in A Tree Grows in [name_u]Brooklyn[/name_u]. I think it’s a very nice name, but if you haven’t read the book you might not get the connection
[name_f]Eleanor[/name_f] with either middle name-- classic, and could have the nickname “Nora” which matches very well with [name_u]Nolan[/name_u] and sounds similar to [name_f]Isla[/name_f].
[name_u]Or[/name_u], [name_f]Nora[/name_f] on it’s own if the middle name is [name_f]Claire[/name_f]
Lila/Lyla with the middle name [name_f]Claire[/name_f] – very similar to [name_f]Isla[/name_f]
[name_f]Lola[/name_f] with the middle name Claire-- similar to [name_f]Isla[/name_f] and [name_u]Nolan[/name_u]
[name_f]Lily[/name_f] with either middle name-- pretty, and sounds somewhat like [name_f]Isla[/name_f]
I’ve never actually met any Islas in real life, so maybe it isn’t even that common anyway:)
With [name_u]Nolan[/name_u], I’ll suggest:
[name_f]Lilia[/name_f] [name_f]Claire[/name_f]
[name_f]Lyra[/name_f] [name_f]Claire[/name_f]
[name_f]Adele[/name_f] [name_f]Clara[/name_f]
[name_f]Heidi[/name_f] [name_f]Claire[/name_f]
[name_u]Juniper[/name_u] [name_f]Claire[/name_f]
[name_f]Thea[/name_f] [name_f]Claire[/name_f]
[name_f]Pearl[/name_f] [name_f]Clara[/name_f]
[name_u]Delaney[/name_u] [name_f]Clara[/name_f]
[name_f]Elise[/name_f] [name_f]Clara[/name_f]
[name_f]Tallulah[/name_f] [name_f]Claire[/name_f]
[name_f]Soraya[/name_f] [name_f]Claire[/name_f]
[name_f]Maia[/name_f] [name_f]Claire[/name_f]
[name_f]Bronwen[/name_f] [name_f]Clara[/name_f]
[name_f]Anja[/name_f] or [name_f]Waverley[/name_f] 
I think [name_f]Isla[/name_f] [name_f]Claire[/name_f] is lovely! I also think it sounds very nice with [name_u]Nolan[/name_u]. [name_f]My[/name_f] vote goes [name_f]Isla[/name_f] despite the growing popularity.
Other ideas:
[name_f]Irena[/name_f]
[name_f]Briony[/name_f]
[name_f]Eliza[/name_f]
[name_f]Violet[/name_f]
[name_f]Soraya[/name_f]
Never thought of these! Thank you!
Similar vibe/sound to [name_f]Isla[/name_f], [name_f]Anja[/name_f], and [name_f]Alana[/name_f] is [name_f]Ayla[/name_f]! There are also lots of different spellings of the name to choose from. [name_f]Ayla[/name_f] [name_f]Claire[/name_f] would also be a beautiful combo!
Congratulations!
Personally I wouldn’t let popularity deter you from choosing your favourite name. [name_f]Isla[/name_f] works wonders with [name_u]Nolan[/name_u] the overall sibling set feels very fashionable and cool. I did think [name_f]Ayla[/name_f] could work as an alternative to [name_f]Isla[/name_f] she has a similar sound but definitely isn’t as popular. [name_u]Nolan[/name_u] & [name_f]Ayla[/name_f] work really well together they feel fashion forward and unexpected as a pairing. Also [name_f]Ayla[/name_f] has that strong ‘a’ sound a lot of your other ideas also share. I think [name_f]Ayla[/name_f] [name_f]Claire[/name_f] would be great.
Good luck
If our next baby is a boy, we intend to name him [name_u]Nolan[/name_u]. Our daughter’s name is [name_f]Annie[/name_f] [name_u]Marion[/name_u], if that provides you with any inspiration.
Other name ideas based on your post:
[name_f]Alayna[/name_f]
[name_f]Ann[/name_f]
[name_f]Ariah[/name_f]
[name_f]Autumn[/name_f]
[name_f]Dorothy[/name_f]
[name_f]Eleanor[/name_f]
[name_f]Elise[/name_f]
[name_f]Elizabeth[/name_f]
[name_f]Eunice[/name_f]
[name_f]Freya[/name_f]
[name_f]Jewel[/name_f]
[name_f]Joanna[/name_f]
[name_f]Kenley[/name_f]
[name_f]Kiera[/name_f]
[name_f]Leanna[/name_f]
[name_f]Lita[/name_f]
Luelle
[name_f]Lulu[/name_f]
[name_f]Madelyn[/name_f]
[name_u]Marie[/name_u]
[name_f]Matilda[/name_f]
[name_f]Rose[/name_f]
[name_f]Stella[/name_f]
[name_u]Sydney[/name_u]
[name_u]Teagan[/name_u]
[name_m]Til[/name_m]
[name_f]Tilda[/name_f]
[name_f]Tillie[/name_f]
[name_f]Vera[/name_f]
[name_f]Vivi[/name_f]
[name_u]Vivian[/name_u]
[name_f]Isla[/name_f] is so pretty ! If you are looking for close alternative have you considered
[name_f]Ayla[/name_f]
[name_f]Ines[/name_f]
[name_u]Esme[/name_u]
[name_f]Selah[/name_f]
[name_f]Aida[/name_f]
[name_u]Alba[/name_u]
[name_u]Alma[/name_u]
From the names you listed I love
[name_f]Gemma[/name_f] [name_f]Claire[/name_f] or [name_f]Elowen[/name_f] [name_f]Claire[/name_f]
[name_f]My[/name_f] name is [name_f]Alana[/name_f] and while I LoVE my name sometimes the different pronunciations and spellings drive me crazy ! [name_f]Alana[/name_f] [name_f]Claire[/name_f] is really pretty and flows well though
[name_f]Lorelei[/name_f]
I like [name_f]Elowen[/name_f] [name_f]Clara[/name_f] as a combo! [name_f]Alana[/name_f] is nice too. [name_f]Gemma[/name_f] gives me almost the same vibe as [name_f]Isla[/name_f] (I could see [name_f]Gemma[/name_f] and [name_f]Isla[/name_f] and [name_m]Lachlan[/name_m] as siblings).
I also like the suggestion of [name_f]Briony[/name_f]. [name_f]Briony[/name_f] [name_f]Claire[/name_f] is lovely.
[name_f]Ibbie[/name_f] [name_f]Claire[/name_f]
Inisse [name_f]Clara[/name_f]
[name_f]Ilona[/name_f] [name_f]Claire[/name_f]
[name_f]Iselin[/name_f] [name_f]Clara[/name_f]
[name_m]Tima[/name_m] [name_f]Claire[/name_f]
[name_u]Taran[/name_u] [name_f]Claire[/name_f]
[name_u]Tiernan[/name_u] [name_f]Clara[/name_f]
Rilo [name_f]Clara[/name_f]
I love your boy names! [name_f]Isla[/name_f] is beautiful, and I think you should go for it if you love it, but here are some names that you might like to consider.
[name_f]Maeve[/name_f]
[name_f]Fia[/name_f]
[name_u]Shay[/name_u]
[name_f]Mona[/name_f]
[name_f]Elva[/name_f]
[name_f]Brenna[/name_f]