I think Maria would enjoy LJ Smith. Vampire Diaries is obvious, but I bet she'd also love The Secret Circle or one of the Night World volumes. The latter are loosely connected but can be read independently; I'd start her with volume 1, though. They are similar in subject and style to Twilight, but with way scrappier female characters.

For Madison, try When You Reach Me, by Rebecca Stead. It's a middle-grade time-travel story that handles the paradoxes very cleverly; I think it would appeal to logically-minded kids. It's also really funny and well-written.