If Norman Rockwell were alive today, his iconic Saturday Evening Post illustrations might star not Mother and Father with their children, but rather blended families featuring step-parents and step-siblings. “The so-called ‘blended family’ is no longer an aberration in American society: It’s a norm,” the American Psychological Association wrote in 2019. How, then, can blended families navigate holiday celebrations most smoothly? An expert from Sag Harbor weighs in.