The Joel Files?

Though nobody in the Joel family was killed by Nazis, it does make me think that the film may be loosely based on the documentary The Joel File
http://www.imdb.com/title/tt0310601/

"Beate Thalberg's critically acclaimed documentary tells the story of two German families, whose ways first cross in the 1930s. Karl Amson Joel owned the fourth largest mail order company in Germany, but has to leave Germany with is family due to his Jewish roots in 1933. Meanwhile, the Neckermann family gains his business empire by profiteering from the Nazi expropriation laws. Almost seventy years later, their descendants, among them pop star Billy Joel, meet in Vienna to confront themselves and each other with their common history.."
http://www.imdb.com/title/tt0310601/plotsummary