Complex sentence: Oppenheim's second marriage (1957--76) was to Ellen Adler, daughter of Stella Adler; they had a daughter, Sara, and a son, Thomas, who became president and artistic director of Stella Adler Studio of Acting.
Split into simpler sentences: Oppenheim's second marriage (1957--76) was to Ellen Adler, daughter of Stella Adler. They had a daughter, Sara, and a son, Thomas, who became president and artistic director of Stella Adler Studio of Acting.