This was a *tough* battle. I'm not sure if you all will consider this cheesing out, but it was the way I beat em.
Summoned two Mord. Swords and two Skeletal Warriors (then hasted and blessed them), and one Animal (War Dog) Moved my whole party out near the bridge except for Edwin /w boots of haste, stoneskin, imp. invis., and magic resistance. Then I moved the dog up to be sacrificed, while at the same time moving Edwin out the door, and leaving the summoned swords and warriors behind (in each corner of the room).
The Demon Knights then appear, but by this time Edwin is through the door and has shut(!) the door behind him. Carnage is going on in the demon room now. The plan was to wait a bit, and then open the door with Edwin and cast some Abi-Dalzims to finish off the Knights, but as soon as I opened the door, Edwin got nailed with a Power Word, Fear (I shoulda cast resist fear!!) and became useless.
There was still one Sword and one Warrior left fighting the knights (and getting destroyed), so I decided to just rush in there and finish it while they were distracted. I cast stoneskin, spirit armor, imp. invis, fireshield, mirror image, blur, negative plane protection, and tenser's transformation on my character (dualled Kensai/Mage), kai'd, went in the room and just absolutely wasted the demon knights. I probably just should have done that from the start, would have saved time
Not sure if any of the above could help you, Jeannada, but it was fun to remember anyway.
As for this little fight not being worth it if you don't use war hammers, or the 'evil' two handed sword, I disagree. You can still use the girdle, which, IIRC boosts strength to 21, something ANY party can use.