For Rosalie, I wanted the 'Rose' part and I wanted it to be a name that could be vaguely French. Belvedere is basically a stock name in architecture, literally 'beautiful view' in Italian, but I wanted it to have something to do with New York City, and there's a Belvedere Castle in Central Park, which made sense with Sleeping Beauty being a princess.
Evie (Eva) was because I have a friend whose name is actually Greta, which was too close, but her sister's name is Eva and I liked it. Also, Eva means live, and I've always thought that survival was one of the biggest parts of Hansel and Gretel, first with getting stuck in the forest and then with the witch. Hollis was random.
Nina is for Eponine, but it also means girl, which was appropriately non-descriptive. It needed to be something slightly Spanish, since she's something like a quarter through her father, plus she's from a Mexican-American gang that runs drugs up from...Mexico. Castel/Castillo are variations of each other, basically with the meaning of working in a castle, which I picked because of Cosette's song.