“The Spiegels, who died eight years ago, left their art to their two daughters, who each received half of its estimated value. For this month’s auctions, one chose Christie’s and the other, Sotheby’s—though not without intrigue within the houses themselves. The companies expect the works could sell for more than $160 million, the two largest art consignments of the bellwether spring auction season. The dueling auctions on May 17 and May 18 illustrate the challenges of valuing estates involving art, as well as the hard edges and personal animus underpinning what might seem a genteel business.”