Sefer Chofetz Chaim chapter 8 halachos 10, 11

Halacha 10: You may not speak lashon hara to anyone whether it’s a non-relative or relative unless it’s for a positive reason. For example, you can tell your wife that it might not be a good idea to lend anything to a certain person but he or she is known not to give or pay it back. The same is true with two business partners or the like, one can tell the other that it might not be wise to do business with this certain person because he’s not going to pay you. Even if you don’t know firsthand of this problem but you have heard rumors you can still tell them to be careful because they aren’t allowed to believe what you say, just be concerned and take proper precautions. That being said you should tell them in a way that will make it sound possible and therefore be cautious but not decisive so that they will feel they can actually believe you. An example in Chazal of this type of warning is in Kiddushin 52b where the students of Rebbe Meir was warned not to enter a certain area because people might start up with them. The Chofetz Chaim bemoans that many people confuse this halacha and talks about his day with his wife including about people that started up with him in yeshiva or work. Besides the lashon hara being said your wife will most likely take it to heart and will start to not treat this person and his family nicely and she might not only belittle the person who started up with you but she might look down upon you and start making fun of you after a while. This is based on an Avos diRebbe Nosson 7:3 which says that you shouldn’t talk too much with your wife which refers to not telling her all that happened to you during your day because it will just cause fights and she will look down upon the person who started up with you and will look down upon you as well. Even if she will find out eventually what happened you shouldn’t say anything because the victim tends to exaggerate.

Halacha 11: No difference who you speak in front of whether it’s a non-relative or even a relative, a brother should not even talk about another brother in front of his parents unless he rebuked him first and the brother didn’t listen, or he knows the brother won’t listen to him but might listen to his parent to change his bad ways. We know this from the case of Yosef and his brothers. Yosef was punished measure for measure for speaking lashon hara about his brothers to his father, even though he did it so that their father will rebuke them. And although he got it wrong and really, they were doing nothing wrong so he was punished for not looking more into the matter. However, the Chofetz Chaim says it’s true that even for bad things your siblings really did you shouldn’t run to your parents to tattletale if you can fix the issue yourself.