These few 4-5 chapter is the weird arc that I can't understand what the author wants to show...
MC is pretty much dealing with the less loyal noble that didn't try to overtake by armed force. That noble grand ducal family was trying to take over the kingdom through means that aren't strictly bad on paper (i.e. marriage), but would still resolve to use "cheats" if needed.
It's the kind of thing I've actually saw/read about in other media and that actually worked to some extant. One time, the person doing the mind control/hypnosis poses as an ally for an arc or two until she made a "last minute" mistake that revealed the entire plot to all the people in the audience. While on another, the plot was never discovered, MC got killed (and reincarnated) with the once prosperous kingdom now falling to shambles.
But though luck for the grand ducal family, they are in a story with an OP protagonist that can smash through political play by force. It's not a story were one's has to outplay their adversary through wit and luck alone or loose because that don't have what it takes.