“Killer Twin” (*1/2 out of four) was a killer mistake about two twin sisters separated at birth (both played by Lindsay Hartley) and one who finds the other and sees she will literally kill for her identity and her life. Hartley is good in a dual role but plotholes and contrivances abound and make you wish they may have stayed separated. For a more intricate and complex look at the same subject, watch “Brothers” or “Single White Female” instead.