Anime

I don’t know what they were planning to do by poisoning, but not killing, and kidnapping Myne.

I got the impression that they weren't trying to poison her, just drugging her unconscious to make the kidnapping easier, but the drug they used reacted badly with her existing congealed mana issues.

For this episode… why did grandpa become comically dumb for that scene? A strange bit of slapstick comedy, I suppose.

That's a bit of wtf from the anime's perspective, but Bonifatius is supposed to have always been like that. He's a musclehead who doesn't completely realize his own strength, especially when he's emotional. But unlike, say Angelica, he's not really even normally that much of an idiot. It's just like he has this big blind spot, and that's why you heard in this episode that he was warned off of touching Rozemyne, who would be easy for him to accidentally kill, just randomly.

In this episode, it wasn't animated for obvious reasons, but when Bonifatius punched the attacker in the hallway, it actually bashed his head completely in, and IIRC, that guy's body struck and killed another attacker. He basically just killed them because he was upset and there were enough of them that killing some wouldn't make a difference. And again unanimated for obvious reasons, when he unmasked Joisontak, he is supposed to have accidentally ripped off part of his face.

If I’m following correctly, I think the use of the secret passage is the first piece of evidence that specifically indicts Georgine as assisting in the immoral schemes of the pro-Georgine nobles.

That's not absolutely proven to the Archduke's family, so they don't really have that evidence. If they did have the evidence, they'd have executed two nobles instead of one. So, really, the use of that passage is only a supposition that has been animated just for the audience. And from the audience's perspective, we already have seen some of the immoral schemes of pro-Georgine nobles, like their plotting against Wilfried.

Also, I don’t think I understand why the evil noble has to sneak out to give Myne a poison and give the kidnapper instructions himself. Is it a needless event to implicate the evil noble and Georgine or perhaps there’s a good explanation?

edit Looked it up:

Joisontak wanted to kidnap Charlotte or Wilfried and then heroically save them himself to get brownie points with Rozemyne. He was an idiot. Gerlach gave him the Ahrensbach soldiers he still had tucked away from the Noble that tried to get Myne in Part 2. That's how he knew of the kidnapping plot and took the opportunity to kidnap Rozeyne herself. To Gerlach, Charlotte was just the bait and distraction he needed to get Rozemyne for Georgine.