Question: Is it true that there is a unique relationship within one's family even if there are harsh disagreements?
Answer: Yes. Family is unique. Ha-Rav Moshe Tzvi Neriya related that Ha-Rav Moshe Leib Shachor was a regular visitor to the house of the Brisker Rav, Ha-Griz Soloveitchik, and also one of the great admirers of Maran Ha-Rav Kook. Rav Shachor tried to explain to the Brisker Rav, how Maran Ha-Rav Kook brought those far from Torah closer and how he publicly led in this spirit. But the Brisker Rav's way was diametrically opposed, and he did not accept his explanation. Rav Shachor saw that the Brisker Rav harshly criticized the leaders of the Mizrachi in general and specific individuals in particular, but he never mentioned Ha-Rav Meir Bar Ilan, the Netziv's son in his old age and one of the Mizrachi leaders. Furthermore, when Rav Bar Ilan would visit, the Brisker Rav would warmly greet him. Rav Shachor asked about this behavior, and the Brisker Rav said: "R' Meir is my uncle"! Rav Shachor took the opportunity again to explain Maran Ha-Rav Kook's leadership, which along with his fundamental philosophy, also included a deep love for every Jew, and he added: "To Rav Kook every Jew is considered an uncle..." (Moadei Ha-Re'eiyah p. 306).
We once heard Ha-Rav Herschel Schachter (Rosh Yeshiva at YU) relate in the name of Ha-Rav Zevulun Charlap (who served as Dean of RIETS Yeshiva at YU and as a Rav in the Bronx), grandson of Ha-Rav Yaakov Moshe Charlap (Rav of Shaarei Chesed Neighborhood in Yerushalayim and one of Rav Kook's closest students), that this story with the Brisker Rav and Rav Shachor was known in his family. Rav Charlap added, however, that the Brisker Rav said that while Rav Shachor's understanding of Rav Kook was sharp, it was not according to the Halachah. After all, there is a concept of one's seven closest relatives for which there are special Halachot based on the verse: "From your flesh (relative) do not turn a blind eye" (Yeshayahu 58:7), and not everyone is considered a relative.
It is possible to answer the Brisker Rav's difficulty, however, based on the Gemara in Shabbat (105b) which says that when a Sage dies everyone is his relative, i.e. everyone tears his garment over a Torah scholar's passing (see Shulchan Aruch, Yoreh Deah 340:6). And if everyone is considered a Torah scholar's relative in his death, it is all the more so true in his life.