If you read the book Frank says that him, Kurt and nicky in the past had helped hide the money in the second wife's house they knew where ut was.

I mean the dad battered Kurt because he was unhappy with the divorce it got so bad only nicky the brother said enough and by the 90s nicky stopped hanging out with him. Frank senior is sick

I recommend the book it was really good gave an insight into why he flipped and how crazy Frank senior was