The False Prince and Princess

What if it wasn't just Sage who was picked up by Conner at Mrs. Turbeldy's orphanage? Maybe he had a mischievous (but slightly calmer) twin sister who was his partner in crime. What if Roden and Tobias also had twin sisters, and all were competing for the thrones of Prince Jaron and his twin Princess Marianna?
Rose is Sage's younger twin by five minutes, which he will never let her forget. Though she helps him with his trickery and thievery, she isn't as incorrigible and is at least somewhat civilized but not all that much.
When they are discovered by a regent who wants to use them to take the throne of Carthya himself, the twins must learn to remember themselves while being trained to be someone else.