Back to the Ackerman situation, I think we're all aware about the classic road rage syndrome when it comes to considering the familial relationship between Levi and Mikasa, and at first I wanted to start out with the notion that maybe the term "branch family" isn't understood, but then on checking on the english, once again I also wonder whether it's because the translation makes it a bit more ambiguous as to what Kenny was talking about.
(...but people (yatsura=fella(plural) smh) who interfere with their business (trade) showed up there too... in any case... it looks like they remain poor)
(I forgot the ellipsis in front the first time round, and thought I'd show both versions anyway)
But this is the term Kenny used:
And some useful links I found on reddit to explain what this is about:
How do branch families work? Like what are they?
How does the main and branch family thing works?
and the perhaps too technical wikipedia article on this, on the other hand, they have prominent and I suppose equally confusing real-life examples:
The other information that I thought was missing was perhaps the lack of sense that the Ackermans are Somebodys, but no, I feel like this one is clearly in the manga:
Although "warrior family" has no meaning in english, and again, I hope that this will help:
Or if you want a deep dive, I'd attempted a translation of the japanese wikipedia article on this a long time ago.
But put the two things together, this is why Kenny knows about the branch family. In a family that's important and prominent enough, for hereditary purposes, they do need to know and be able to trace all the branches of the family lineages.
I guess it's just that we don't have enough royal watchers in this fandom to know about and be able to explain this XD, but I do feel like the information being bandied out there about Levi and Mikasa's relationship doesn't even come anywhere close to any of this, and it's in the manga itself, one doesn't even need the Answers or any other guidebook for this information, however, it's not just obscure, it feels like it's absolutely unknown, and what we have is just a lot of loud and valueless voices on the subject.
But the fun and awesome take from this (or maybe not so fun and awesome for some) is that if Levi's line dies out (status unknown) then Mikasa's family effectively becomes the House of Ackerman ;)
But tl;dr, they are known to be related not because the families are close enough to know about it but because the Ackermans were important enough people to keep track of all the connected bloodlines.
But also, just to make things clear, here are the charts showing without a doubt that they are unrelated for an unspecified number of generations as well. I'm sorry I couldn't find my nice version of the answers one, this one is a rehash from when they have some promotion for an exhibition (I think but cannot confirm that it was the final exhibition), but it's pretty much the same thing. (Don't know why head/main family (本家 honke) and branch family were taken out of the translation, they're definitely in the Answers guidebook as well, I checked.)
(Usual disclaimers apply :)