I still really like Zoe with your girls' names. I know it doesn't start with a vowel, but man it just makes so much sense with those other names. Really Zoe sounds great with all of those middle names, but I think I like Zoe Jean the best. Its so great!
Some vowel names that I think sound the best with Olivia, Addison, and Ella:
Ione/Iona nn Onie (That's what my grandma was called!)
Indiana nn Indie
Indigo nn Indie
Imogen nn Immie
Isabel nn Izzie
Other names I think would sound great with Olivia, Addison, and Ella:
Lillian (I know it was an option for a middle name, but why not kill two birds with one stone? It also looks great with their names.)
Some names I would avoid:
Eva/Eve - Too similar to Ella
Isabella - It literally has Ella in it
Sophia - The ending is too similar to the ending of Olivia
Elena - Sounds similar to Ella
Try to avoid nicknames that could sound like your daughter's nicknames in general.
Here's some combo's that I like:
Zoe Jean, Zoe Michelle, Zoe Ann
Waverly Jean, Waverly Michelle, Waverly Ann, Waverly Elise
Lillian Michelle, Lillian Jean, Lillian Elise
Molly Jean, Molly Ann, Molly Elise
Uma Jean, Uma Lillian, Uma Elise
Indiana Jean, Indiana Michelle, Indiana Elise
Indigo Jean, Indigo Michelle, Indigo Lillian, Indigo Elise
I think a really unique way to go (for vowel name) would be Uma! Otherwise I really recommend Zoe--sorry!