The entire castle is under their thumb and that means the kitchen as well he can't not eat and thats why he will have to eat the poison as well
So why can't he just kill that blond bastard?
Because nobody outside the castle knows what kind of a man Duke Truyde is he can't just kill a prominent and influential duke "just because he wants to" also most people have no faith in the king thanks to all the rumours he would have no supporters
Huh, yeah i guess that makes sense
Why can’t the king just not drink the potion or stuffs with potions? It’s not like they can force him ?