I didn't say this before, because I tend to think about these sorts of things differently than most. But we have no information that suggests that his father's wishes were 'Don't give any of this money to your sisters'. And there are definitely ways he could have done that. If he has an estate and left money to anybody, that means he could have added any stipulation he wanted about how to the money is to be spent. But he chose not to do that.
The ONLY thing we know about the father's wishes as it relates to the money he had was 'When I die, the money goes to my son'.
it's an assumption that the father wanted his son to not give his sister's anything after he died.
He's not wrong either way. Because it's HIS money. But for me, his father's wishes about his own money become irrelevant when it's no longer his money.