i want some conformation on some stuff...
if my memory serves me right, Miyuki is using shiba as her family name because Maya ordered her so right? but is it true that she will change her last name to Yotsuba after she graduate? i kinda forgot about this one but i do believe someone once posted about it.
Shiba is her actual surname. Kuroba is an actual surname as well.
It's not because Maya gave that order but because Yotsuba Clan handles like that the family structure, with only one Yotsuba known while others have another surname. Maya is the only Yotsuba know with that surname because she is the head and a public figure.
Miyuki once is ascended as the Leader will take the surname as inheritance of the title, but not because she was born with it.
That they are all Yotsubas is a thing, but the family structure prevent others to link anyone with the clan.
By any chance, it al started with the Dahan's incident, and it does not seem like a tradition. If there was a male instead of the twins Maya and Miya, we can only speculate what the scenario could have been, since the children take the father's surname.