Double Act — Jacqueline Wilson

Ten-year-old Ruby and Garnet are identical twins who do everything together. Especially since their mother died three years earlier. They dress alike, wear their hair the same, and sit together in every class. In fact, everything about them is the same--except their personalities. Ruby is funny and outgoing, Garnet is sensitive and shy. Together they're the perfect double act--and that's just the way they like it.
Soon the twins' life is turned upside down. Their dad has been spending a lot of time with his new "friend" Rose. Ruby and Garnet can't stand Rose. To make matters worse, Dad and Rose buy a bookstore out in the country and the whole family moves. Ruby hates their new school, but Garnet thinks it isn't all that bad. When Garnet befriends some of their new classmates, Ruby feels betrayed and stops speaking to Garnet. Garnet misses her sister terribly, but has to admit it's nice doing things on her own for a change. Somehow, the girls will have to find a way to maintain their special twin relationship without spending every minute of the day together.