I believe Cinderella's family name in the Disney version was Tremaine. I know people like to attribute that to just her stepmother, but odds are that "Lady Tremaine" is the title the stepmother acquired upon marrying Cinderella's father, rather than a title she brought with her. (Not impossible, just unlikely) So I'd use that.
Aroura I'd have to dig up if they gave any further characterization to Stephen's realm beyond his being king, but I don't think they did. I'd have to watch the movie again and see if I could pick up anything from the heraldry.
Snow White - okay, here I'd seriously have to think, because there's so little to go on in the movie. probably just pick a Prussian noble family name and go with that.
Ariel would get some variation of "from the sea" or "of the sea" ... not sure what language, probably Dutch.
Belle... Belle should have a family name, but it's possible that it's never mentioned (and between the animated movie, the live action movie and having helped with a high school production of the play, the various lines of dialogue are getting muddled in my head.) Without it being mentioned, I'd try to find the french translation of "Tinker" as in "Tinker about" or "fiddle with the mechanics"
Mulan has one (Fa or Hua)
Alice has one (Liddle, though that's knowledge outside the movie.)
I'm pretty sure Tianna has one (sad to say I haven't watched The Princess and the Frog to the point of memorization yet.)
And I think most of the Pixar generation ladies have family names, except perhaps Rapunzel. (For Elsa and Ana, it helps to read Futhark and know Icelandic naming rules.)
