The Donatello Triplets
From the television series The Golden Girls. Singing group played by the real-life singing del Rubio triplets (Eadie, Elena, and Milly) in the "You Gotta Have Hope" episode (02/25/1989). They're managed by Sophia (Estelle Getty), who agrees to let them play in the hospital variety benefit show if they also take her boyfriend, a lame magician act.
The del Rubio Triplets played another fake band, The Wanker Triplets in an episode of Married... with Children.