Is it confirmed that Mirabella, Corpse, and Froggy are the only potential wives in the game?

No, there are more wives.

Somewhere in the dwarven underground, you get a quest to save a dwarf's daughter from a cyclops cave. After you do it, you can marry her. Though I didn't mention she's as attractive as a pile of garbage, but it's a matter of taste :)

Also, there's the elf chick :D

And the demon girl.

Bleh. Now I have too many kids. I hope they grow up or something cause I don't want them all !

do they grow up in the game? :-P

Can you switch between wives.
 

After you divorce a wife, can you re-add them later on?

What are the bonuses of later wives, such as the dwarf and the demon? I'm not entirely sold on the ones I have available (the zombie & the frog), so I'm wondering if I should wait or if I should marry now to get the bonuses.

Edit: And how far in is the demon wife?

Ya, its random as most of the things in game (including availability of troops and enemy troops you encounter)...

No once divorced, they are gone for ever...

i am mage and i got +3 int from the frog wife.