More like nobody would have noticed otherwise. And the protagonist didn't throw a fit over it, keeping it even more off the radar. So it's not right to judge the entire industry on this one particular case.
That's not Kamo's grandma, it's Granny Kamo from the next town over that isn't related. But they know each other since Kamo-kun sometimes gets her mail by mistake. See chapter 10.
Starts with a similar premise as "Climbing to The Top of the Esper Academy" by EBA. It's hentai though, so content filter settings might block it if they're enabled for you.
Speaking about a monarch in the 3rd person would be "his majesty" or "her majesty". "Your majesty" is when you are speaking to them directly. Same goes for "highness" for other royalty, like princes or princesses.
Empty boxes in manga = scene transitions. Like fading to black/white. Basically saying "stuff happened between the previous panel and the next one that's not important enough to show."