The Fortas Chamber Music Series at the Kennedy Center is featuring three concerts this week emphasizing ensembles who collaborate. The Emerson String Quartet and Kalichstein-Laredo-Robinson Trio perform on Tuesday the 15th. On Wednesday the 16th, it’s the Orion String Quartet and Windscape. And on Thursday the 17th, the Juilliard String Quartet joins their protégés, the Afiara String Quartet. Classical WETA’s Marilyn Cooley had a chat with the Juilliard Quartet’s second violinist, Ronald Copes.