The Martin Sisters
Singing duo from the 1950 film, I'll Get By, set in 1939. They're not really sisters, and their names aren't really Martin.
They sing for real bandleader Harry James (playing himself). Aspiring songwriter Freddy Lee knew Terry Martin, and tries to get them to sing his song.
Terry Martin's name is really Hortense Heinberger (played by Gloria DeHaven). The other member is Liza Martin (June Haver).