Liv and Maddie is a Disney teen sitcom about identical twins Liv and Maddie Rooney. Though both parts are played by a single actress, Dove Cameron, it actually requires three actresses to make it work. When Dove is playing one of the characters, a body double stands in for the other role, and it's through the magic of camerawork and editing that enables the two characters to appear as twins.
Both Liv and Maddie have individual actresses that act as Dove's body double - Emmy Buckner is the body double for Liv and Shelby Wulfert is the body double for Maddie. Neither actress play the double for the other character, and neither Dove, Emmy nor Shelby are twins in real life.