Mona Nerenberg (owner of a shop in Sag Harbor, NY that is recommended by Ina Garten) and her wife, landscape designer Lisa Bynon’s four-bedroom cottage, Redbrook, sits on three acres of land in the hamlet of North Sea. Built in the 19th century, there was once a fish market on the property. Today, with the help of interior designer Mark Cunningham, a former VP of creative services at Ralph Lauren, the cottage is bright and airy, with new windows and a beamed ceiling to brighten up the kitchen, white walls and glossy white floors intermingled with seagrass and wicker, and white wisteria and rattan chairs awaiting on the terrace…