Well the demon’s army is now royally screwed. Terrible leadership is the fastest way to self destruction. They’d probably lose to the humans now without the MC interfering (but as an added bonus they’ll probably piss off the mc in five seconds). It is pretty annoying that all this came to pass because the heavenly kings fell for an obvious trick and were subject to a stupid silencing spell. Clearly no one with a brain wants the idiot, weaker, but somehow more aggressive brother to be in charge. This all being the result of an misunderstanding, which will eventually have to get cleared up and won’t last, is pretty annoying. I’d have preferred if he handed the throne over to someone component and was able to leave the responsibilities of it and could permanently move on to the next stage of his life (he clearly wants a quiet life with the woman he loves like the MC). 
This is just going to be an annoying little arc that propagates idiot moves by the new leadership to make more artificial conflict for the OP mc that can solve anything in seconds. I’m still pissed that the former hero hasn’t been brutally murdered yet and has been instead given a woman that honestly loves him despite his many, many evil deeds (as if mass murders, near world enders, and just straight up jerks deserve a redemption arc (well a “well, I guess I’m good now” arc)).