
Question, was it ever explicitly stated that the Todaroki children other than Shouto are weak?

Nope, it was more along the lines that they weren't "perfect". He specifically sought out a powerful cold type for his wife because the weakness of his fire type was overheating. He wanted a perfect child with both fire and cold who could use their power without limit by continuously cooling/heating. It's not that they were weak, they just didn't have that balance so I think the reference was them as "failed experiments". I don't remember which episode it was, sorry.

Dabi being a Todaroki is just a theory. Given what we know so far, it is a plausible background for this character. So I don't think believing or hoping that he is a Todaroki is foolish. You're just working with the information you currently have. Until the author actually reveals Dabi's past history we're free to go with whatever theories we want.

For me it would make sense that the Todaroki family would be powerful since both the mother and the father have powerful quirks. With this in mind, even if the other Todaroki children are not chimeras like Shouto, I would expect them to be able to defend themselves adequately. So it surprises me that Natsu is basically helpless against this villain.

What chapter was that because I don't remember Natsuo's power being mentioned? The closest thing I can think of is just the flash backs into how the father rejected all the kids except Shouto because they didn't have the kind of power he had been looking for. But then I don't know if that means they were weak, only displayed their mother's power, or were strong but didn't seem to be strong enough to surpass All Might.

Hyesung's behavior is why I struggle with this series sometimes. We're at chapter 71, at this point he and Dojin have a kid, are bonded, have married (voluntarily) and Dojin sincerely loves him. Yet over and over he treats Dojin like crap and I sit back wondering why Dojin even bothers to keep trying. Prior to them bonding I don't understand why Dojin wanted him (again, taking into consideration Hyesung's treatment of him). I've come across tsunderes in stories before and I've been fine, but for some reason Hyesung's character can be grating on my nerves at times. I wish the author would let him evolve a little more so that it's not just Dojin putting in the effort to make the relationship work.

Does anyone know how often this series is released/updated in Japan? (1x month, every 2-3 months, longer?)

It’s sporadic
https://lhscan.net/manga-kono-oto-tomare.html

Even though the MC of this series is Hinata, Furudate built up the other characters enough that I cared about them and what happened to them. They were not just background characters whose names I could barely remember. So having this time jump that suddenly rips away all of those lovable characters is quite jarring and sad.

While I can honestly respect an ending that doesn't have the main team win, as long as it was a good fight, there is something about this ending that feels unsatisfying, incomplete, and a let down.
I've been following this series for years. I started buying the official hard copy (even though the English translations got on my nerves sometimes) because the series was just sooo good. But this is how the author chooses to end the series? . . . I mean I knew it was possible that the series wasn't going to continue into year 2 for Hinata and Kageyama, but I was really hoping that everyone was right and we'd see another year.
I wonder if Furudate is ill or something. Some of the art has been looking a little off from past work and this sudden rush to kill off Kurusano when she could have easily had Kurusano fight Fukuradani (and possibly lose there) makes we wonder if something is up.

Not since Princess Nine have I been disappointed by an ending so bad. Crimson Hero confirms for me that shoujo and sports don't mix well. The sports side of the story seems not to be taken seriously. The MC is inevitably going to be obsessed with some guy and her relationship with him is all that's going to matter. The sports side and all that that entails - drive, passion, focus, your team, honing your skills, being your best - will eventually come down to being just drivel because the guy is the real goal and trophy.
It's funny, I keep thinking Kouta is short (or should be short) but he's actually one of the tallest members in the club and often when Sane let's his hair down I don't recognize him (⌒▽⌒).