It took me 2 tries to kill those gargoyles on Tactical difficulty. It wasn't that hard but you definitely have to use a couple of heal potions. I'm guessing you haven't spent your skill points well or at all. At that point I had my deathknight with one-handed slashing..damage +1 and accuracy +6. I figured since damage over +1 wasn't much of an increase, I'd make sure I was hitting a lot. The other room I had no issues at all with though. Have you gone to the battlefields at all to level up some?