The plaintiffs in the case include Thomas, Jaris and Peter Rockwell, the sons of Norman Rockwell, who object to the sale of two of their father’s works, Shuffleton’s Barber Shop (1950) and Shaftsbury Blacksmith Shop (1940), which the artist gave to the museum. Both paintings are due to be auctioned at Sotheby’s New York American art sales on 13 November, and are estimated to make a combined $27m to $40m.