The Taurus Demons are just protecting the Chaos Ember which you don't necessarily need at the moment. It's definitely time to switch from Quelaag's sword and start using a better scaled stat weapon with what I'm assuming is Dex since you're using that sword. Spears are sometimes good for this. I'm partial to the Winged Spear.

But for Dex weapons I always fall back on katanas like the Iaito that's hidden just after one of the entrances in Blighttown and the Uchigatana which you can get from the merchant in the Undead Burg if you kill him. You can also buy it from Shiva of the East if you're part of the Forest Covenant. He shows up in Blighttown on the bottom by the mill looking thing. The Washing Pole is also good and can be bought by Shiva. Just upgrade.