Ubiquitin, I don’t agree with all of your examples. Eruv is a pure halachic shailah, and FWIW, some well known poskim completely rejectct the validity of the eruv no matter what your rav says.
Similarly, I think eating in the house is an absolute no-no, it’s just that I can’t argue with the process of following rebbeim (maaseh rav) against the Shulchan Aruch when those rebbeim clearly believe in following halachah 100%; it’s the specific application I’m arguing with. Hence, I can fully respect that the person thinks they are following halachah while at the samextime thinking they are wrong.
Again, the reason talmidim were told to sit in the succah is that not doing so is a mistake in halachah (see Aruch Hashulchan for a strong possibility for how that mistake happened) and the fact that it’s the family minhag doesn’t mean a thing against a clear halachah.
I think everyone agrees that minhag doesn’t trump halachah, the disagreement is about what suffices to allow the assumption that the minhag is in accordance with the halachah.