So far: Kyoko and Michi/Kidou are cousins. Kyoko is taken in by this family after the loss of her parents. Now, in canon, Kidou's adopted/lost his parents early on. I wouldn't mind making Michi also adopted if that's easier? But I'm good with whatever works. As is this is already a weird family.

Also I should mention this guy is very loyal to family and that'll cause some wonderful drama. It did with Kageyama, and he wasn't even a relative.