Lucifer: Most likely lead singer or keyboard player
Mammon: Guitar player or backup singer
Levi: Dancer or bass player
Satan: Wouldn't be a performer but the manager of the band
Asmo: Lead singer. He'd want the spotlight on him all the time
Beel: Drummer
Belphie: Bass or guitar player
Diavolo: He's fin with anything as long as he gets to participate.
Barbatos: Keyboard player
Simeon: Backup singer or guitar player
Luke: Drummer or dancer
Solomon: Keyboard player or guitar player