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It's possible that all your choices are either already popular or poised to become popular. Oliver, Leo, and Emmett are all riding popularity waves right now, and haven't peaked yet. Only Charles isn't in a peak, but it's still a solid choice of a name, about as popular nationally as Jack (although Jack + Jackson is about twice as popular than Charles).
If possible, try to see what people are naming babies in your neighborhood/town. They're going to be the names you're competing with on the playground, and in your son's classes, and so the greatest potential for overlap are there.
I think the big thing about men preferring the names of people we grew up with, is mainly due to the fact most men aren't exposed to present naming trends because they aren't around children. So, when they think of children, they see their peers when they were children themselves; that's all they've got.
Definitely Saoirse Ronan is the way to introduce the name.
Your husband likely doesn't know any Saoirses other than Ms. Ronan, so making sure he both knows who she is and how to say her name (a "making of" video or talk show appearance video or whatever helps immensely there) will help greatly.
You want that good association with the name, call up images that he'd be proud to have in a daughter but not too worried about protecting. Thankfully, Ms. Ronan does project that image quite well.
It's one of those Anglicization things. Hypatia is originally more akin to hi-pah-tee-ah (with accent more or less equal), but under English phonics, hi-PAY-sha is more expected.
The name that gets the worst of it? Agnes. It's from French, where it's pronounced more like Anya.
Because, let's face it, expecting English speakers to speak imported words and names as originally spoken is quixotic.
You know, your comment about names for a baby boy made me wonder: are there good floral names for boys? I mean, yes, I get the whole societal association of flower = pretty = girl, and boy = please don't be delicate = stick to hard things, but I bet there's more to it from there, if you go by sounds.
Would names like Gladiolus, Jonquil, Oleander, Anther, Crocus, Arum work? This might be more in the realm of character naming than baby naming, but I bet there's some space here for it.
Otherwise, back to floral names for girls, Acantha, Salvia (or Sage... Sage would work on a boy, too, come to think of it), Erica, Cyrilla... I'm running out faster than I expected.
How about Okera?
Here's a few more possibilities?
Anton, Roman, Dominic, Luther, Emmett
Mixing and matching something along these lines leads to Emeric, Robert, Uther, Andrew, Ludwig...
I'd like to know more about your husband's interests. For example, if Serena (Williams?), Sabrina (Teenage Witch?), and Lydia (...Heroes, maybe?) are pop references, I'd like to know from where, because that will also inform on what other references would need to be avoided.
If he's worried about Sylvia being foreign, and you're worried about Elaina/Elena being foreign, then I might suggest avoiding the ends-with-a rule altogether. There have been some broad convergent trends in naming around the world (Emma and Sophia are popular everywhere), but -a endings do tend to do better in Spanish-speaking cultures. Part of the reason I say this is that a way to cross Lydia with Lyla and still keep the nature theme is the name Lily, even though it's more popular now in Northern Europe.
If you're looking for a name that (as far as you're concerned) is not trending, and (as far as he's concerned) sounds pretty and is not weird, then you might consider popular name lists from 20 years ago. Given names like Brooke, Tessa, Serena, Sabrina, Audrey, etc., you might find something there of interest.
I'm reminded of the Allegory of the Cave, which may be the earliest version of the concept of world-as-projection, which over millennia morphs into the concept of the virtual world. From there we see a whole common motif of cyberpunk take form, all stemming from a concept developed in antiquity and now readily visible everywhere.
And so, there's a name that's "on trend," but would never be used. It's a name everyone knows, but still stands out as unique, different. There's no doubting its pedigree.
For their son, I recommend Plato.
I'll admit that the first thing on my mind when hearing Violet and Rose was a Keeping Up Appearances reference: "Where's Daisy and Hyacinth?"
That said, it's definitely a sibset with a clear theme with a pedigree, so I don't think it's a problem.
My mind immediately split the difference to suggest Analytica Lemma. Don't listen to that.
I think Veronica Laura has the best cadence of the choices, and I'd go with that. The "-a Emma" combo is a potential tripping point, as is "-a Ana-".
I could imagine Peregrine making a comeback today, if someone is looking for a compromise between a softer-sounding name and Falcon.
I love Gwendolyn. I'd love to see it get more use.
Lily and Sophie stand out as names that are popular in Germany now and for school-aged children in Australia. Furthermore, they're on the Icelandic list. However, would they feel German to an Australian?
One other name that checks all these boxes, and has the added benefit as a compromise choice for a vetoed Elsa: Ella.
Non-Biblical, goes with Charlotte Olivia, like Levi or Eli, fairly traditional?
Oliver, Valerius (nn Val), Basil, Alfred, Evan, Eugene, Ivar, Ignatius, Liam, Leo?
Zeke is the classic nickname for Ezekiel, and yet it still carries rakish appeal today. I say go for it.
I'd have expected to see Circe on the list. Perhaps not a real siren per se, but she is definitely heavily associated with all manner of sea creatures.
Speaking of which, a super-daring but on-trend name would be Scylla.
I have to ask: Would "A bear eats a berry" repeat?
Subtle Halloween names?
Catrina sounds normal enough, but it's also the name of La Calavera Catrina, the famous illustration of a female skeleton dressed up that has become the main symbol of the Mexican Dia de los Muertos. Unfortunately, it would have passed muster in Anglo communities until Hurricane Katrina.
Kali has gained traction despite popular depictions of the Indian goddess.
Although Samhain is well-known enough as the Celtic pagan source for Halloween, it's actually pronounced closer to "Savin" or "Sawin."
The big thing is to remember that Halloween is just the first day of a three-day Catholic holiday: All Hallows' Eve (aka Hallowe'en), All Hallows' Day (or All Saints Day), and All Souls' Day. As the vigil to all the saints and holy, there's a lot of subtle references that can be made in that space.
I feel like the real issue is that -LINE is probably not a trendy pronunciation in your area, so people are going to assume that that's not the way to pronounce Emmeline, no matter how you spell it. It's likely down to being in a -LEEN pocket, like others have said.
In any case, you most definitely did not name your daughter wrong. Her name is Emmeline, and others can adjust, once they know the pronunciation. In many ways, it'll be a blessing. You (and she) will be able to tell from the moment they mention your daughter's name whether they're someone who knows her or not.