I think
Charlotte nn
Lottie is really cute, and I love
Juliet too, but
Charlotte Juliet doesn't sound too great together. It's too choppy. That aside, it goes well with
Vivienne Claire. I don't think
Juliet would get Romeon and
Juliet jokes, and as a middle name most people will never know it anyway.
Nell Juliet - gorgeous, but I think you need a full name for Nell/Nellie.
Eleanor Juliet or
Penelope Juliet would be really nice.
Josephine Juliet -
Love the alliteration!
Matilda Juliet - This is probably my favorite and pick out of these. I think it goes fine with sister's name, and
Matilda is very underused. And
Tillie is really cute.
Some other ideas:
Alexandra Juliet "
Allie" (I prefer
Alex, but you seem to like more cutesy nicknames)
Amelia Juliet "
Millie" or "
Mia"
Edith Juliet "
Edie"
Emmeline Juliet "
Emma"
Evaline Juliet "
Evie"
Genevieve Juliet "Genny" or "
Evie"
Honora Juliet "
Nora"
Katherine Juliet "
Kitty"
Magdalene Juliet "
Magda" or "
Maggie"
Rosemary Juliet "
Romy" or "
Rosie"