Disclaimer: This was done in about half an hour of clicking around on the Demon Level, so this doesn't go into much detail. In addition, I don't really get along with the skills so far, so I don't have information as to what skill did what - sorry.
Enemies deal 2 damage both to the heroes and to the villager. Therefore, I was mistaken - the villager doesn't have higher defense than the heroes, just much higher HP.
The Maximus with the enormous sword deals 80 damage to the enemies at first, then 120, then 160, and then 240 for the rest of the level (both with melee and ranged attacks(. I have no idea why - perhaps he's 'leveling up' behind the scenes?
The 'burn' from some flame skill or other does only 4 damage each time it activates.
The Cheryl with the wand has her melee attack do only 160 and then 180 damage, but one of her magical attacks does either 360 or 540 damage. The poisoning-effect here is much better than with the fire spells, as the darkness-poison effect does 25, 30, or 45 damage. (I think I've seen all three damage numbers.) I noticed that she One-Hit KO'ed a Treasure Whelp or two, though I do not know which skill this was. (I was letting the AI cast spells rather than selecting them myself.)
The Maximus with the Kunai does 120, then 160, then 200, then 240 damage with his ranged attack. After this, I've decided that the damage levels seem to be the same for the heroes regardless of weapon, and thus stopped testing them.
Either the Shadow skills are much more powerful than the Flame skills, or the developers have implemented the promised resistance of the Whelps to fire. Whichever it is, I think those trying to kill as many enemies as possible on the Demo Level should use Shadow skills as much as they can and to put the Maximus with the enormous sword [who only has flame skills available to him] as near the enemies as possible so that he uses melee attacks instead.
The repeated "2"s from the monsters went by too fast for me to even estimate how much HP the heroes and villager had.
Two 240-point hits seem to take off half a Red Whelp's life bar, so I'm guessing they have about 240x4=960 HP each. Meanwhile, the Treasure Whelps have a non-visible amount of HP left after two 240-point hits, so I'd guess they have 500 HP. This explains the OHKOs I saw earlier, as they must have been 540-point hits from whichever Shadow skill she was using.
Just some numbers, since we don't have stat screens yet. :)