Richard H. Hepburn, 89, a playwright (whose work was not widely performed) and younger brother of Katharine Hepburn, 93, died Wednesday at the Connecticut home he shared with his sister. “I don’t know if playwriting was his most brilliant gift,” his niece, playwright Katharine Haughton (who, as an actress in 1967, played Katharine Hepburn’s and Spencer Tracy’s daughter in “Guess Who’s Coming to Dinner”), told the Hartford Courant newspaper. “I think that although he spent time with his playwriting . . . the center of his life was living.”