It's a very tough fight for sure. Try to keep them separated from each other, concentrating on one at a time (as after you have killed one of them, the other will get their energy back). Use the breakable pillars to your advantage.
Also, if you're hoping to go for Platinum trophy or 1000/1000 in the game consider taking Smough out first now, and then Ornstein first in NG+. Ornstein is a bastard in his 2nd form on NG+. Something to consider if you are going for all weapons in the game.
Try summoning Solaire too, as he will distract one of them so you can concentrate on the other. He's a bit shit though really and won't last long, but it will certainly help. Also, try summoning humans back on the bridge outside (where you come down the elevator and see the first Gargoyle). It's quite busy for summoning there, and they will be able to help you. I wouldn't recommend trying to summon by the bonfire as there isn't much action there (not in my experience at least).
Good luck, it can be a fucker of a fight but it's a damn good one!