I like davisellu's idea of Eleanor nickname Nora. Leora (I like this spelling) is too similar to Lena for my tastes. Charlotte and Penelope would also go with Lena.
I'm not quite sure what your style is when it comes to boy names since you said the names for your twins were chosen for meaning more than anything else.
anything your style?
My daughter goes by Adalena probably 95% of the time because she has recently asked to be called by her full name so I'm not sure that the Lena/Leora problem would be an issue, The only thing she has NEVER gone by is Addie.
I LOVE Penelope, but my DH isn't a fan. I don't think he would go for Eleanor either, but maybe Nora.
From the other listed so far I also like:
Do you all think Emerson is now considered more of a girl name or still pretty acceptable for a boy?
My husband also like Deacon for a boy I think it's ok but i just don't love it! and he likes Grace for a girl.
Leora/Liora is way too close to Lena. And you said you don't have a middle name for a girl picked out, or you don't plan on one? Since the other two have middle names, I think its important for the third child to have one too. So if you have a girl, save Leora for a middle name, or use Nora as the first name instead.
Adalena, Charlotte, and Nora make a lot of sense together.
Good middle names for Nora:
And Emerson is becoming a girl's name too, but what isn't now? Emerson makes more sense as a boy's name, since it litterly has "son" in the name. If it bothers you though, Emmett would be a close alternative. Oliver is also really cute and handsome, and goes perfectly with Adalena and Charlotte.
Oliver Ezra is a really cool choice. I personally like Oliver Henry or Oliver Edward, as they seem to match your girls' middle names well.