My... uncle-in-law (is that a thing? It's my father-in-law's brother)
I've always figured you can make up whatever relationship is necessary for the situation, as long as you follow the established "rules" for such things. Years ago, our neighbor Kevin was into model railroading, had a pretty nice layout, and we bonded a bit over that (plus our mutual love of prog music - he's the guy who took me to see Rush Counterparts at the Capital Center). One time he showed me the latest issue of Model Railroader magazine, and it featured a big writeup on the new layout from one of the foremost guys in the hobby, Bruce Chubb. I took a look at it, and said "Yeah, I've seen that." The new magazine? It just came out. "No, I've seen the layout. He invited us over for an operating session a couple of months ago."
Kevin just about lost his shit. "You ran trains on this layout? How do you know Bruce Chubb?" I told him that Bruce is my step-uncle-in-law. He's the brother of the guy that my wife's mom married. She's a widow and he's a widower; it was the second marriage for each of them. I'm pretty sure that "step-uncle-in-law" isn't used very often, but that's who is he is to me.
And since this falls loosely under "Benefits of Home Ownership", let me tell you a little bit about this layout. Bruce and Janet built their new house specifically for the basement. Well, they didn't build it themselves, but they had it built from Bruce's design. He's an engineer (electrical, not the kind who drives trains, although he's done that, too). The house is a single level, three-car garage at one end, kitchen, living room, dining room, library, Janet's craft room, probably some other rooms I'm forgetting, and bedrooms at the other end. The house seemed to go on for acres. And the entire basement below it, including under the garage, was the
"train room". It is mind-blowing. Through custom circuitry of his own design, each operator is assigned a train, and the box they hold controls that train. Throttle, brakes, horn. My son drove a train for half an hour, through mountains and towns, and barely covered a fraction of the layout. This was 25 years ago; that level of tech hadn't been invented yet. Well, actually it had; Bruce is the guy who invented it. He designed the circuit boards that people still use today.