Mr. GOH!

I play a melee tank outfitted with Havel's gear usually, but had to substitute in a bunch of lighter stuff so I could maneuver. I attacked Ornstein first with a black knight halberd. Once smough powered up, I switched to a longbow +5 and large arrows and kited him to death. This was after maybe 25+ attempts at tanking them in Havel's armor. I couldn't move fast enough against either super form and kept dying.

I beat them alone as well. Took me many tries but the trick was to be as mobile as possible. Blocking wasn't as effective against them as being fast and dodging.

I was able to beat them by myself as well. I came close quite a few times, but eventually I was successful.