A prestigious French family of art dealers stretching back five generations faces half a dozen lawsuits with allegations of fraud and stolen paintings. The Wildenstein Institute—the family's research center in Paris—has been raided several times with investigators carrying away sculptures and paintings by such artists as Degas and Rembrandt Bugatti. These works had been reported missing by Jewish families who claimed their art was stolen by Nazis, and wealthy heirs who said their treasures disappeared during family estate settlements. Guy Wildenstein, 65, the current president of Wildenstein & Co., is at the center of the controversy and is being sought by French anti-fraud investigators for alleged tax evasion and money-laundering, in addition to possible theft. Another twist in the scandal: Wildenstein and his brother, Alec, allegedly convinced their stepmother that their father died bankrupt to rob her of money from his estate.