Hilchos Lashon Hara chapter 8, section 13
The Torah warns us not to believe lashon hara. Briefly, the rule is that every Jew is commanded to not believe lashon hara said of any Jew unless he is a heretic, informer, or suchlike, who are not considered as being with you [in Torah observance].
Hilchos Lashon Hara chapter 8, section 14
It makes no difference if one hears lashon hara from non-relatives or from one's parents or household. We even see in Tana Debei Eliyahu (ch. 27) that if one sees one's parent speaking superfluous words, such as lashon hara, besides being commanded to not believe them he must also make them stop this behavior. (He should be careful to do this respectfully as I write in Be'er Mayim Chayim). If one keeps quite, he and they will be severely punished.
The sages say (Shabbos 54b) that if someone can rebuke the people of his household [and does not do so] he is punished because of them in the world to come. Therefore a person should often rebuke them [for wrongdoing], doing this gently and explaining the great punishment of the next world and the great reward if one refrains.
One should be very careful that one's household does not ever hear one disparaging people, for besides the prohibition of lashon hara, he will now never be able to stop them from speaking lashon hara as he does so himself. Generally, the household's behavior depends on that of the householder.
