Possible Clues:

• The Andrews Sisters, e.g.
• Wynken, Blynken and Nod, e.g.
• Chamber group
• Troika
• Donald Duck's nephews, e.g
• Crosby, Stills & Nash, e.g
• Charlie's Angels, e.g.
• The Bee Gees, e.g.
• Crosby, Stills and Nash, e.g.
• The Stooges, e.g.