Love Rosemary, used to be my number one fav, now it's in my top three. I adore it. It's so beautiful. I think it sounds AMAZING with Scarlett and Malcolm, especially Malcolm (which I LOVE).
Rosemary Anne doesn't have the best flow, but it's not that big of a deal. I do love Rosemary Annora though.
Rosemary is a bit classic, and a bit hippy(in a good way). It reminds me of an old antique lace wedding gown. Exquisite. Any Rosemary I would have would be a blue-eyed blonde so this is how I see a little Rosemary.
I prefer Rosy as a nickname, but Posy isn't horrible. I prefer Posy as a nickname for Josephine. I myself want to use Rosemary Josephine, nn Rosy-Posy. How about Rosemary Josephine Anne, nn Rosy-Posy?
I don't think nicknames have to flow with last names.