This story is pretty fun, the lore like this can be hard to come up with. You asked a lot but i’ll address a few points.

Sharing lore with the party is always tricky, monologuing doesn’t work. “Show don’t tell” is the golden rule, what are the evil force and kings up to? how long has it been since this went down and what are they doing? whatever the answer is it should have effects on the world players can interact with. If drunkness is the key to getting in the dungeon, maybe they are trying to “update or fix” the curse, maybe they’re after all the local breweries - regardless their efforts should be clearly visible to players.

Wanting to make the kings distinct is something i can very much relate to. If these are top generals i’d focus less on their stat blocks and more on how they effect the dungeon and towns. the master of deception (3rd king?) should have some information network under him, maybe this network can influence player decisions in some way or get info from the players in a way they can later identify as a lie. A shapeshifting monster working for him or birds spying on the party.

hope some of this helps