Possible Clues:

• Trio
• Triumvirate you need time to look up in a book
• One more than a couple
• Chekhov's sisters, for example, see mother being abused
• Putting prophet up in model dwelling results in triangular relationship
• Here's to me performing with the trio!
• Bronte sisters may be hard on Welshman in book
• Not a properly constituted company?
• See mother running round triplets
• Magi making a crowd, they say? Not many