This Troper is writing a story that centers (mostly) on a family like this. The head of the household, Kyou, is aging and his identical twin sons Kenta and Katsuro (the older of which (Kenta) lives with him since he doesn't want his elder son moving out) are squabbling over who will get to inherit everything once he dies, and the feud has passed on to their sons, Kenichi (who is the youngest child in his family) and Kaito (who is the oldest child in his family and five months older than Kenichi). However, the family
doesn't follow a typical
patriarchal structure and instead focuses on seniority, meaning that the real third in line after Kenta and Katsuro is Kenta's daughter Kaori. On top of that, it is hinted that Kaori and Kenichi's sister Kasumi (middle child) is actually some sort of HumanoidAbomination, (her NotSoImaginaryFriend, Violet, who
looks exactly like her, certainly is) and might not actually be related to the right side of the family to be an heir. And on top of ''that'', everyone in this world has
unrealistically colored hair and eyes and the family follows ThemeNaming (which you probably guessed since all the names start with a K) which they take
very seriously.