Just summon someone to help you. I consider it fair, since it's 2x2, and that's by far the hardest fight in the game (well, I don't have the DLC, so I don't know if there's something harder there).
Theoretically you can get pretty wrecked by that Undead Dragon as it's way harder at that point in the game, but at least you can run away from that one. (The one on the ledge, not the one in the sewers)
Don't lock on, kite around the room until they are separated enough that you can land a few hits on Smough before Ornstein rushes over. Roll into all of Super O's attacks except the lighting stab to hit him, stay near his ankles. Gl.
Go after Ornstein first, make it so that you are always facing Ornstein with Smough behind him (so you can easily react to both, plus Smough needs to catch up before doing anything and this gives you time).
If you get a bad position, just run away and try to bait Ornstein into a good one. The RNG can screw you over here, but just roll/run until you get a comfortable position.
The fight has no tricks, it just takes a lot of good reactions.
You can also go against Smough first, this will make the first phase much easier, but the second phase will be a completely different beast. It may be worth it to just try going after O since Super Smough is much easier.
DD Info - PSN: Steel_Tarkus | Mami | Level 140~ Sorcerer | Scather/Challenger | Would appreciate a Blessed Flower.