I'd assume based on your descriptions the Faerie dragon descends from the Purple Dragon. Accurate?
IIRC, Faerie dragons are small. I actually didn't read the fluff on them, but they're probably more closely related to pseudodragons.
Mirage dragons (another Feywild dragon) are specifically mentioned as descendants of Green dragons who lived in the Feywild.
How's the Gray? Is he sick? Does he sneeze ooze and vomit phlegm? Or is he more majestic than that?
Grey isn't majestic. The fluff isn't; they're rapacious hunters, to the point some become mercenaries to hunt down specific targets.
They also have a terror aura, and are spiked all over. I believe there's an ability in the back you can replace their breath weapon with. The Purple dragon can also lose its bite in exchange for some sort of psychic hammer (I was unsatisfied with the amount and levels of the alternative abilities).
There is one ability that (I believe) the Death Mask dragon has which is sexy. The power hits a PC, and when the PC attacks the dragon, the PC also takes half damage he deals to the dragon.
running a dragon-oriented campaign?
There is a mention of Dragon-centered campaigns. It's in the ToC; I didn't read it, but the subheading dealt with Famous dragons, and Famous Dragonslayers.