I believe that for both Monk victories on those dungeons, I prepped Binlor. Both the extra knockback damage and magic resistance help a LOT. On Namtar, prep Quest Items because the soul orb/viper ward are great, and save your reflex/quicksilver/WHUPAZ for the second form. VS is a matter of luck with getting a tolerable monster mix and good items, but I don't recall anything being terribly tricky.
I don't recall how I managed Namtar with a Vampire (probably Dragon Shield I assume) but I remember that Vampire + VS was the very last of the Vicious dungeon combos I finished (VT and goat excepted). It's brutal. I prepped Zot, and this was back in the area where Zot + WHUPAZ had the powerful combination--although I finished with some resources left, so who knows, I might have managed. The monster loadout for that dungeon is just so hostile. You'll probably need to try many times to get a tolerable monster mix. Prep Quest Items because the Balanced Dagger and Platemail are both great.
I have not finished any Vicious dungeon with a goat, so good luck there!
I did VT VS with a Sorcerer I believe, and then later (because I got it confused with Dragon Isles) I did it with an Orc Wizard as well. Once again, Binlor is awesome for this dungeon. You don't have to do anything fancy or weird; just play carefully and with some luck and it's manageable.