Isekai by Moonlight

[robkelk]

Canonically, Mamoru is already an orphan.

As for the others, current plans are for there to be three family names in the Mizuno extended family, and you already know that "Mizuno" and "Kino" are two of them. The third is one that the affected characters have not used on-screen as of the end of chapter 4... and anything further than that would be a spoiler, so only one of the prereaders knows.

EDIT: If you really want character spoilers, there just might be a few on All The Tropes, depending on how much attention I paid to what I have and haven't published when I updated the page. I see that a character who's had one line so far is on the page, so he must be more important than just an extra...