Two years ago, when the old Federal-Italianate residence at 6 Union Street in Sag Harbor finally escaped the years-long grip of bank foreclosures and landed in the hands of real estate developers, it was in a state of near collapse. Its windows were boarded, the front porch was in danger of caving in, and there was a hole in the roof of an addition at the back. The building, which is thought to date to the 1760s, has long been called the Morpurgo house, named for Annselm and Helga Morpurgo, the sisters who had lived in it, fought over it, and let it disintegrate over decades.