Is slandering one's honor considered mere talk, and should parents avoid whoever slanders their son?

If the parents of your divorced wife unjustly slandered [your parents], they have committed an injustice and a grave sin. Your parents should not boycott them, but they must denounce the wrongdoing, for the Prophet, peace and blessings be upon him, said: "Whoever among you sees a wrongdoing, let him change it." And he said: "Whoever defends the honor of his brother in his absence, Allah will turn away the Hellfire from his face on the Day of Resurrection." If these individuals do not repent, and boycotting them is more beneficial, then that is preferable. And if you have evidence of their slander, you have the right to take the matter to court to have the Hadd punishment for slander applied to them.