Changelings (The Twins of Petaybee, Book 1), by Anne McCaffrey
This follows after the Petaybee books by Anne McCaffrey. (Powers That Be, Power Lines, Power Play) It focuses more on the twins than the adults as they grow up. There's a lot of them trying to be more independent, but they also have to figure out who they can trust with their true natures.
I think I'd be hard pressed to find an Anne McCaffrey book that I didn't like and this one is no exception. I love the universes she creates.