Hi Sophie,
"pure bloods" and "consumers" are most likely "normal humans"
I don't think Old Georgie is explained explicitly (although it has been years since I read this!)
As for the first question: best not say!
The book has a structure which takes you to the post-apocalyptic centre and then brings you all the way back out all the way to Adam Ewing; it finishes each part as it goes. It does give you a lot of answers in this fashion (obviously, as every section ends on a cliff-hanger up until this point!)
Mitchell has said of the book: "All of the [leading] characters except one are reincarnations of the same soul ... identified by a birthmark. ... The "cloud" refers to the ever-changing manifestations of the "atlas", which is the fixed human nature. ... The book's theme is predacity ... individuals prey on individuals, groups on groups, nations on nations."
In essence, what I am saying is: your questions will be answered best by the text!
Have you ever read Number-9 dream by David Mitchell?
All the best
Spare Ed