Dynasties: The Elliotts Series by Susan Crosby

The mysterious "lady in red" who appeared at his Manhattan apartment inflamed his senses and ignited his passion, but John Harlan's new lover was the very woman he could never possess: his ex-fiancé's twin sister, Scarlet Elliott. Scarlet had loved John from afar for years...and one night she succumbed to her urges and made her way into John's bed. But could their relationship ever be more than a forbidden affair?