Kalameet is the only one that uses fire, and frankly - I don't expect a shield to do much against his fire. Even the gods of Anor Londo were afraid of him.
Granted, the gods of Anor Londo weren't much to begin with. Especially so if you accept the idea that they aren't even really "gods" at all, but giants who posed as gods to rule over the "pigmies" (humans).
No, I think they were actually deities. A good comparison is to Greek Mythology in that they are quite supernatural in ability, but still have similar traits to humans, especially in how they interact with each other. They're definitely not all giants either. Gwyn is much smaller than any of the giants you encounter. Gwyndolin and Gwenevere are certainly not giants either. That was quite an illusion of Gwenevere, I doubt she was actually really that big. The only giants that we can verify for certain is Gough and the smith in Anor Londo. Gough was one of Gwyn's 4 Knights. Along with Ornstein, Lord's Blade Ciaran and Artorias. Those three aren't giants. They're not human either though. Probably some lesser deities or demigods. I suppose you could make the case that Smough is a Giant, but there's no hard evidence of that. There's also Bishop Havel the Rock who is definitely not a giant - although he's not in the same class as Gwyn's family or his 4 Knights either. He was probably just a really boss Bishop.
You also have things like the Dark Ember whose description refers to Occult weapons as being used to hunt the gods. And occult weapons do extra damage against many of the residents of Anor Londo. When the flames began to fade as a result of the spread of the Dark Soul, the gods began to decline. Clearly there was a plot to kill them which resulted in so many dangerous things (to the gods, i.e. Priscilla and the Lifehunt Scythe) being locked in the Painted World. Lastly, if you read the description of Ring of the Sun's Firstborn it mention's Gwyn's firstborn as being a god of war.
There's no indication that I can find that the leaders of Anor Londo (or their knights) were simply imitating Gods to rule over something. I think they really were deeply flawed and temperamental deities similar to Greek Mythology, but distinctly different from any other humans/giants/etc.
Giants most definitely existed - you meet the Giant Blacksmith, and Gough is another one. But he mentiones them being old, and dying. See: Tomb of Giants. Those giant skeletons didn't come out of nowhere.
The four knights were instrumental in hunting the dragons. Which happened a very, very long time ago. That makes me wonder about Ornstein... is he undead now? Where has he found Smough?
Occult Damage does additional damage against any "living" enemies, which includes Silver/Black knights as well as humans should you choose to kill them.
Priscilla, to the extent of my knowledge, choose to live in the Painted World to get away from the regular world. She is a half-breed and never felt like she belonged. This girl is coo-coo.
Gwyn's Firstborn was the Sun God, whom you worship as the Sunlight Covenant. The reigning fan theory, with which I agree, is that Solaire is the mortal remnant of that deity. A lot of his dialogue, and his item descriptions, hint in that direction.
As for Anor Londo, Gwyndolin is the only remaining god. The Silver Knights are illusions, but when "real" they are the original guardians of the forbidden city. Black Knights are Silver Knights who left with Gwyn to rekindle the flame - literally 50% of the knights left with him. They were scorched by the flame, and became Black Knights. Gwynevere is, obviously, not real and others are long-gone.
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For the dragons, just wanted to point out that Kalameet's flame is in fact 50% magical 50% physical. I had to switch around my shield set up (a mild obsession of mine in the game) just for him.
Gaping Dragon is, according to a fan theory, a dragon who was corrupted by stray humanity ie. dark soul. He resembles a human inside a dragon, and always hungers for more - just like humanity.
Everlasting Dragon, if I'm not mistaken, is not a true dragon but rather an avatar of dragon power.
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Dragon Crest Shield, by the way, was wielded by a mortal knight. This might imply that humans of that age have mistaken large wyverns like the Hellkite to be true dragons (may be a prod at modern dragon imagery, which is weak and silly compared to ages past)