Wow, that was strange and humorous! Immediately after reading your list I thought "
Sylvie Louisa would be absolutely beautiful!" and then I read everyone else's posts. I think most of us would agree that this combo is amazing.
Heidi would go nicely with
Ramona, but (and maybe it's just me) there seems to be something missing there. I think a different name would work even better.
I don't care for Harlow,
Harper, or
Sienna, and
Lux is nice but doesn't fit very well at all.
Jacqueline would also work well.
My personal associations with these names on twin girls, though, aren't very good. I think of
Jacqueline as pretty and sweet but maybe a little stuck up, while
Ramona sounds like the older, slightly less attractive but highly intelligent and free-spirited twin. Like I said, these are only my personal thoughts based on people I've known by these names. But it's why I really like
Sylvie Louisa (or even
Louisa Sylvie) best: the names even each other out. One doesn't seem more pretentious than the other and together
Ramona and
Sylvie sound absolutely adorable!