Hmm.. I think it'll work out. I think the problem will be more how they will all hang out once it becomes public knowledge. Because their safety may be at risk. It may become known at 10MC in the next arc, but not publically known until after high school. That's what I hope b/c once it's publically known, the life Tats and Miyuki currently live will not be possible.
Erika already knows (from the arc with Lina). She doesn't know specifically what position Tats holds within Yotsuba, but she knows he's connected enough with them that he can get information at a level that means he's not a lowly minion. Plus his power and Miyuki's power are top class which hints at a blood connection. So she's guessed, though nothing was specifically said between her and Tats.
I can just imaging Erika beating up Miki and Leo if they changed their behavior to Tats. And then they'd come around. An opportunity for comedy. Mizuki would surprise us all and think it's romantic or something. Honoka may be shocked, but her elemental loyalty would kick in and where Honoka goes, Shizuku will accompany.
Mayumi has already guessed that Tats is a Yotsuba extra. And in a way, he is. Except that the Yotsuba don't strip their extras of their number and banish them (my guess here). They probably use them as training fodder and if they survive, they become useful tools. But her reaction to him being a guardian and Miyuki being the niece of Maya will be interesting.
Masaki's reaction to Miyuki being a high-up Yotsuba will be interesting too. But I think he'll come around, since he's besotted, with the optimistic thinking that there's actually a better chance of marriage between them since marriages between 10MC children is not uncommon (for example, Mayumi's marriage candidates). Especially since he's the heir, he probably can't marry just any excellent magician. He will probably be expected to marry an excellent magician who also brings some sort of power with her (10MC connection). He may even go so far as to think, if Miyuki is the heir, that her leading the Yotsuba will "clean it up" since he can't see beyond her beauty and elegance.
Now, Jumonji may be angry. Since he asked Tats right out. which is interesting since Tats thinks , after the first 9SC, that Jumonji is his natural enemy.
No matter what happens it'll be epic!