So in that example. Given that my family doesnt eat in the sukkah on shemnini atzeres, are you saying I should eat in the sukkah?
Who cares what I would say? I know of two people who were told by two different Litvish roshei yeshiva to do so, and yes, if somehow I were in the position to tell people what to do, that’s what I would say (but I don’t look negatively at someone who doesn’t, although I tease some of my friends about it).
Off the top of my head, I can’t think of any other widespread minhagim that way.