Malbim: For this there is no kinship between fathers and sons, not for merit or liability, in the case depicted - the father was a Tzadik, his son a Rasha, and his grandson a Tzadik.

Radak (6): This refers to a mature son, who is proper for his own reward and punishment. Minors die due to their parents' sins, or receive good due to their parents' merit. Evil adults, their parents' merits will not help them, just like Tzadikim will not suffer due to their parents' sins - "Poked Avon Avos Al Banim... l'Sonai ¹ " (Shemos 20:5). It says about reward "Shomer ha'Bris veha'Chesed l'Ohavav ul'Shomerei Mitzvos l'Elef Dor" (Devarim 7:9). However, the Midah of reward is greater than the Midah of punishment. Zechus Avos adds to the children for 1,000 or 2,000 generations, like Hashem guarded for us, until today, the Bris of our fathers; we love Him and guard His Mitzvos. Even though there are Resha'im among us, today no Jews do idolatry, and most do not do the other sins listed. Hashem promised to guard Bris Bein ha'Besarim forever, and it says "v'Zacharti Es Brisi Yakov v'Af Es Brisi Yitzchak v'Af Es Brisi Avraham Ezkor" (Vayikra 26:42). Those who left our Emunah were not truly from their seed, rather, from converts.

Malbim (20): Just like a father is not punished for his son's evil, so a [virtuous] son is not punished for his father's evil.

Malbim (20): Just like a father's carob tree does not help his evil son, so a father's evil does not harm his virtuous son.