@golguin: I'm currently at about SL 55 or so...I've got a few points into str/dex/end/att for the basics and then am concentrating on faith for the miracles. As far as miracles go, I am using Heal, Lightning Spear, and have pyromancy flame +5 and fire orb attuned. For a shield I am using the Caduceus Kite Shield +10.
Up until this point I have generally been using the Shadow armor, sometimes equipping heavier armor if I need to. I've been trying either the Silver Knight set or the Crimson set for the resists against these bosses but it seems like I'm either slow and get pummeled because I can't get out of the way fast enough, or I'm fast and take way more damage and just die faster. I have been using the poise ring and the phys def ring together.
I don't think the problem is my gear or my build, it's just that I'm not great at the game yet and am especially poor at dodging. Up until this point I've mostly been using block then strike techniques or sometimes parrying, but hardly ever dodging.
I'll try your suggestion about getting more Estus flasks, I didn't even know that was possible!
Once you go down into the catacombs (entrance is at the graveyard area at Firelink with those skeletons) and kill Pinwheel for the Rite of Kindling you'll want to go fight Havel for his ring. If you already have it switch out the phys def ring for Havel's Ring so you could get a boost to your equip load limit. It will allow you to equip heavier pieces of armor with higher Poise. The Wolf Ring with its +40 Poise and Havel's Ring form one of the best ring combos in the game. Make sure to stay under 50% of your weight if you plan to dodge. 25% is ideal. If you still can't dodge just go full Havel armor.
Pyromancy is extremely powerful once you max out your flame. I don't know if your +5 is ascended or if you still need to get it to +15 and then to plus 5, but make sure it's maxed out. You'll want to attune Fire Orb and Great Fireball (take off Heal and keep Lightning Spear) so you can toss out some ranged fire attacks. You can kill them with Pyromancy alone (Great Combustion would replace Lightning Spear, but it's tricky to safely hit them with it by yourself and without Dexterity at 45) if you have your fire glove maxed out.
The last tip is to get your Endurance to 40. If you're not concerned about your level just get Endurance to 40 as fast as you can. If you want to beat them around your current soul level then 25 Endurance is enough for now.