My answer to this rather trollish question was as follows
“You can ask him yourself why he does this and whether he can look you in the eye and say it’s not something to be repented of.
Do not cause trouble in your family by sharing it on. Go direct like a man to your father.”
One Roman Catholic reader responded to my comment as if I had asked the question, and gave one of their answers
“You should explain to your Dad that if you could catch him then so could your mother of sister and suggest that he goes to the Priest to confess his sins. The Priest will be able to grant him absolution.”