Oh Dude!... At no point did I suggest asking/convincing him... his permission is
NOT relevant

I have no idea why you'd think it was!
<<You do know we are vastly superior to him in both social rank and martial prowess right!!>>.
At best he can try to rally a rebellion to oust us from office, but that would only publicise his humiliation, not to mention half the village are our fuck buddies/children and the other half owe us several times over.
<<though I think I'd quite like a rebellion, it would give us the opportunity to finally flex our Goblin King muscles>>
For the night visits I'd do:-
- First night knock him out with a sleepy potion, fuck Jenny... let him wonder about the damp patch in the morning
- Rinse and repeat a few times, maybe draw him into seeing the MC fuck his wife a few times during Debt days, let him adjust to this new level of cuckhood.
- After a few nights have him "catch" the MC fucking his wife at night, but do nothing about it except bitch and moan because he is an impotent pussy.
- Rinse and repeat a few more times, each time he gets more used to it and bitches less until he finally accepts it (maybe gets into it, I'm not sure which way I'd want that to go).
- No more pretence about fucking Jenny when you feel like it. Either kick him out for some privacy or fuck her in front of him... Your choice.
I'd set this up as three sets of loops, with the option to move to the next level of awareness being at the players discretion.
loop 1: Oblivious Cuck (Night, night sleepy head.)
loop 2: Grumpy Cuck (Impotent anger tastes so sweet.)
loop 3: Accepting Cuck/Minion (possibly "Kinky Cuck" Fapping to the thought of his wife filled with your cum)