They're the "witches" in the book A Wrinkle in Time. It might be more appropriate to ask WHAT they are; at one point in the story it's implied that they are the "ghosts" of stars.
Mr. used to be acceptable to address a household by just using the last name, e.g. "Mr. Jones". In modern times, it is typically to use "Mr. and Mrs. Jones" or "Mr. and Mrs. Timothy Jones".