Oh! I forgot to say how much I love Magnolia in my last post. She sounds great with your kids names and definitely feels sweet and dainty if that's what you're going for :)
Also, hove you considered Ingrid or Inga at all? Inga definitely feels sweet and dainty and she goes great with the older kids' names!
I love the 'Isolda' spelling.
Dulcinea – I absolutely adore this for you. I pronounce it dul-sin-AY-ah, so the nn Daisy seems quite intuitive to me, not to mention adorable! Dulcinea Quinn seems kinda perfect for this baby…you've been calling her Quinn the Eskimo, she's number 5, Daisy Quinn is too cute for words, Dulcinea has that elaborate old world feel of your boys' names and the same lacy spunky sweetness as Evi3….the list of reasons goes on.
Svala – I strangely dig this. It reminds me of Svalbard in HDM where the armored bears live, and while I know HDM is probably a negative association for you, Svalbard IS actually a real place: a series of islands in the North covered in untouched arctic wilderness. That windswept icy strength gets a feminine makeover in Svala. I love the winter vibe, I love the exoticness, and I love how fun it is to say. I think she's simple and strong, like Ev3.
Magnolia – I think this matches what you're going for in regards to the feelings and imagery perfectly, and for that I like it. I'm not a fan of the name itself just because I don't like the "mag" sound, but I adore the strong Southern woman vibe. I can't hear the word magnolia without hearing "steel" in front of it, so the name is always associated with a sense of sugar-coated power.
Dagny – I think that if people are going to associate Dagny Tyler with Dagny Taggart, they're going to do so because of the Dagny part. I don't think the T last name has any effect on that whatsoever. Dagny is not a "traditionally pretty" sound, so I think you'll want to use a very feminine middle name to sort of lace it up a notch. Dagny Seraphine, Dagny Shenandoah, Dagny Esmeralda, etc.
My veto points:
Iverine – I know this has meaning to you, and I'm not hating on the name. I just don't think it works in your sibset, you've used all these sounds already. It's like a smoosh of Ev3 and P3r3grine: Eve-rine = Iverine. I vote middle or nothing on this one.
Quenilda – Complete and total honesty? I rather loathe this one :( It sounds like that hedgehog Pokemon Cyndaquil, or one of the wicked stepsisters. I cannot take it seriously, and if I was Quenilda and my sister was Ev3, I would be sooooo upset. I think you need to choose something that is stylistically closer to Ev3 or An@st@sia so that the sisters blend better. That way one doesn't feel like the ugly duckling because she got the clunky unheard-of name while the other's name is short, feminine, and universally recognized.
Rosalind – The perfect mix of delicate and strong. Shakespeare's Rosalind is resourceful, intelligent, independent, and quick-witted. She is the leader of the pack and always true to her family and friends. Plus Evi3 and Rosie? How. Cute.
Damascena – This one may be middle name only material, but it's part of the Latin name for Damask Rose, often used to make rose essential oil. It's unusual, flowy and light despite the heavy look, and has the potential for Rose/Rosie or Daisy as a nickname.
Arden – I know, same play as Rosalind, but I find this name both grounded and romantic. With similarity to words like garden and ardent, it conveys this sort of quiet passion, a deep well, crumbling castle walls wreathed in climbing roses…an old soul. Denna could be a fun nickname, and a nod to one of the best books ever (imho) Name of the Wind.
Lavinia – Victorian, patrician…ancient, even…without being fusty. Lavinia's mythology makes her the mother of the Roman people, putting her on par with the queenliness of sister Ev3. The name is powerfully associated with lavender for me, strong but sweet. Spunky nn options include Vinnie, Lia, Lina, Vina, Nia, and Ava.
Dulcinea- This one is lovely, and the nn Daisy makes it even better. If your concern about it is the length though, have you thought about Dulcine?
Iverine- I agree with Emma about the similarity to your other children's names, but it would still honor grandma in the middle spot just beautifully.
Dagny - Gets major points for being Husband's fave. I think it works well with the others, but I would love to see it with a very very frilly mn.
Magnolia - Gorgeous for a sweet little girl, I am always a fan of it. Many nn's other than Nola but if she ever choses to go by that would it drive you nuts?
Quenilda - I love the idea of your little Quinn, but that's as far as I can go. Quinn in the middle spot would be great but Quenilda is just too much for me.
Svala - This one is not my favorite, but if both of you like it then she definitely has something going for her. I do like that it shares a V with big sister.
Based on your previous 'I name' choices and your love of flowers (surely it has already been considered) but my suggestion would be Iris. Good luck! =]