I called it last chapter, and I'm calling it again this chapter.
The thotubus and the idiot younger brother are going to push all the reasonable and intelligent demons away from the "official" demon army. The coup will be successful, and that will be a catastrophic mistake for them, because it will put every single person the MC cares about on the same side. The old Cryroad King is replaced with the princess, all the reasonable demons are now unaffiliated third parties hanging out with the MC or possibly seeking shelter from humans and demihumans.
The Demon King is actually completely correct. His putting everything on hold to focus on nailing down the MC is the smart play, because any singular wizard who can casually cast Purify can instantly turn any demon victory into total defeat. By putting all of the people he cares about on one side, the younger brother and the thotubus are making a catastrophic mistake. If that happens, the MC no longer has any reason to remain on the sidelines, especially when his lifestyle is threatened.
I suppose the coup could fail, but I honestly hope it doesn't. I want to see the fallout from it being successful.