Fred Jr died of consequences of alcoholism when Fred III was 18 and sister Mary was 16. He’d broken up with their mother 11 years before. Not a great upbringing for them, although Donald’s sobriety is in response to what he saw drugs do to his older brother. Doubt either kid took that lesson from Jr.
Seems typical of wealthy families. Just look at the Kennedys.
So the Donald did a good job of disciplining his children. Whatever he is doing, he's very hands-on. It's working.