1. I think you could avoid
Rosie if you assert yourself and correct people when they call her that.
Rosa would be my first pick.
2. I would imagine that most people who know your middle name are people who know you well, and I'm sure they would know why you chose
Rosalie.
3. If I saw
Rosalie, I wouldn't naturally assume Twilight. However, I notice that
Alice and
Jasper are among your favorites, and if I saw a sibset of
Rosalie,
Alice and
Jasper, I would tend to think Twilight. It's a shame really, because
Isabella,
Rosalie,
Alice,
Edward,
Emmett and
Jasper are all favorites of mine and to use more than one of them in a sibset might get some looks. If you're really concerned, you might try
Rosaline,
Rosalind, or
Rosamund.