I need to know the title or author of these books. They are about people who are shape changers or shift changers or something who can blend in with anything and appear invisible. One book had a girl & a boy who were the same who discovered each other. The guy was in the army or something like that. Seems like there was a circus where the girl was. Eventually they were getting married, I'm not sure whether it was to each other. I think the girl had a twin she didn't know she had, but evenutally found her. The main girl in this book was going to have a baby and I think it was going to be twins. That's all I can remember. Thanks!