Which relatives add impiety to the species of sin?

I know that if you commit a mortal sin against your parents you have to state that in confession. >"Sins opposed to piety are specifically distinct sins from those which offend against charity or justice. Therefore, they must be given distinct mention in confession; thus, for example, to strike one's own father and to strike another man are specifically distinct sins. Any offense contrary to piety between those who are **distantly** related to each other... does not change the moral species of the sin." (Handbook of Moral Theology by Dominic Prummer) But is there a specific limit to how far out the sin of impiety reaches so that you would have to state it?