They had
Nothing you said changes my opinion on that their behavour showed genuine surprise and hurt after Madoff's arrest. So I think they didn't know about the fraud, but my point is that they should have. One of the son's title was something like leader of trading operations.
Back in 2001 there were 2 separate articles (MAR Hedge and Barron's) questioning Madoff's strategy. There is zero chance they didn't read those articles and from then on, they should have asked questions. I understand why they didn't, I just can't accept the answer...