Tochacha is an obligation incumbent and halachicly binding upon every Jew towards every other Jew. Not limited just for their immediate family and talmidim. Whether it is a violation of pritzus or thievery.
If one knows in advance that his tochacha will go unheeded, he is not obligated to go through with it.
See Rambam, Sefer Hamitzvos, ‘Aseh no. 205; Hilchos Deos 6:7; Semag, Mitzvah no. 11; Rashi, Yevamos 65b, s.v. lomar davar hanishma’; Rif and Me’iri on Yevamos 65b; Rosh, Beitzah 4:2; Tosafos, Bava Basra 60b, s.v. mutav; Shabbos 55a, s.v. ve’af ‘al gav; Ra’avid, cited in Chida, Machazik Brochah, Orach Chaim 208; Shitah Mekubetzes, Bava Metzia 31a; Sefer Yere’im Hakatzar, no. 37; Hagahos HaGra, Orach Chayyim 608:4; Sefer Hachinuch, no. 239; Sefer Chasidim, no. 413, Magen Avraham, Orach Chaim 608:3.
Also, see Targum Onkeles, Ibn Ezra, and Ramban on Vayikra 19:17, as well as Rabbeinu Yonah, Sha’arei Teshuva 3:59, 72, 196, and of course don’t forget Shabbos 54b-55a.