Poor choice of words and a misunderstanding about who the creep was talking about, but he had it coming anyway. Besides, whatever he does to him, it isn't anything compared to what the FL would do to him if she had been present.
Poisoning her I get, but growing them within the estate itself? Sure, that is one way to conceal things from those outside the family, but unless it is commonly found in the area, it makes for rather difficult to explain away questions if discovered.
At this rate, whatever else happens, they will be certifiable experts in the location and removal of all kinds of spy devices by the end of this story.
You say he's the weakest magician in the Blackhart family. Whether that is true or not is irrelevant. He's still strong enough to mop the floor with you.
...So the sister went and did the same thing as her younger brother. How many more members of their family are he going to have to beat just because those that already challenged him couldn't accept their defeat and went and lied about it to their family to get them to beat him for them.
Looking? Based on the changes to the knight's schedules, I'd say she is at the very least, a suspect as to the identity of the woman the emperor is looking for.