Meh, I find it kinda stupid that people complaint about a possible relationship between Eugene and Hari. Like, why is it wrong? They are "family" but they aren't blood related, so it's not like they being together would like to children with more genetic problems than an usual couple you'd find anywhere. If they were blood related siblings, then sure, you could argue that is morally wrong and back it up with science, but for people not related to each other, that happened to become family due to outside circumstances... I think the argument of "it's immoral, so I don't like it" is funny, annoying and stupid.
I don't like any of the possible pairings, so as long as Hari ends up happy, I'd be fine with it. Johan is a nice guy, but maybe too nice? Eugene and the other brothers could be cute, but it wouldn't be that interesting. Actually, having Hari get together with green sister (forgot the name of Johan's sister) or even Velontia girl would be interesting. I'd get behind that train.
Though I guess it's because it would be the most dramatic ship in this story. Incest between nobility wasn't all thaaat rare. It wasn't common, but it did happen, though no idea how frowned upon it was. Probably depends on the culture. And if you go with a biblical view of the topic, everything started with Adam and Eve, so there was incest and a lot of it until there were enough individuals for it to not count as incest. And depending on what you call family, incest could actually be really wide spread. People like Charlemagne, Genghis Khan... had many sons and have a ton of descendants rn, so if you say all of their descedants are family (strictly speaking it would be right), then incest becomes a lot more likely.