It's a Great Life (1929)

Sisters Casey and Babe work in a department store that puts on a show every year. As expected, things are going wrong with every act until Casey comes out to help Babe with her song. They are a hit, but in the final act, Casey again comes out and this time the president sees her act and fires both her and Babe on the spot. Benny is able to book Casey, Babe, and Dean into Vaudeville and their act is popular. But before they have their shot at stardom, Dean and Babe leave Casey and the act.