I also agree with the previous posters who really like Camille, but not Cami. Millie is great, though! I'm having trouble coming up with names others haven't put out yet, especially since you guys really seem to like nicknames. I do think Sylvie or Colette would be really pretty additions. But NN-wise... Sylv or Colie? I actually like Sylv, but really hate Colie.
I agree with not being thrilled about Cami; it's my strongest reservation because I have a couple of negative associations with it.
My husband found a reference to Callie/Cali as a nn for Camille. People already assume our "Evie" (Genevieve) is an Evelyn; would that just complicate things further? Or does Callie/Cali seem a reasonable nn to others?
I'm having trouble winning husband over to Millie nn because he works at a school where a student named Millie died a couple years ago; she would have graduated this upcoming year. He feels it might be misinterpreted or be too emotional for the students, several of whom babysit for us regularly.
Do you like Camille nn Mila?
Cecelia could be called Celia and Celie. It still could be confusing, I suppose. Maybe Leelee? That might be too funny.
Girl #4 should have an "ee" ending nn to match Evie, not another ends in A name like Vera and Nora. In my opinion, anyway. Then there is a pattern.
Camille nn Millie is my pick from your list
Some other possibilities:
Carmen nn Minnie
Rosalind nn Lindy
Rosemarie nn Rosie
Irene nn Renie
Camille is my favorite from your list.
I like the suggestion of Mila, and there's also Cam, Mimi, Callie, or really any other pet-name you like. I think too much emphasis is placed on nicknames, and a parent should be able to call his/her child by whatever cutsey name he/she wants, regardless of how close it is to the given name. Most likely when she grows up she won't be going by her nickname, she'll choose to go by her full name anyway.
Beautiful names on all your daughters!