The Sisters Rosensweig, by Wendy Wasserstein

Sara, who lives in London, is a representative for a major Hong Kong bank and is about to turn 54. Her sisters, Gorgeous Teitelbaum and Pfeni Rosensweig, arrive to help celebrate the birthday. Gorgeous is Dr. Gorgeous with a radio-advice program; Pfeni is a world traveler. Various friends and boyfriends also arrive for the party. In particular, Mervyn, a friend of Pfeni's boyfriend Geoffrey, who falls instantly in love with Sara.