Mary Jo was a hero. Her family, not so much.
They could have driven the nails into the coffin of the Kennedy Dynasty, but chose to cash the check instead.
The times were very different. Kennedy family had a lot of power especially in that area. Her family were nobodies and whether or not she was pregnant she was with a married man when she died so am sure they were mortified to dig into it. Also sure it would not have mattered if they had, I do not think it would have changed anything. I am not so sure he even had to pay them off, I think they likely wanted it to just go away.