Are these sentences grammatically correct? (the usage of "everything")
Solution 1:
For answer 1 would probably sound more natural if it were The books were so popular that they were sold quickly. I think everything here almost sounds like it references something other the books, since it would be much more common for the books to be referred to as they.
For answer 2, this definitely doesn't sound right. The use of the word all is a bit awkward because you can't sell some or parts of a book. You can correct it to "The book was so popular that it was quickly sold", otherwise you have to make the book plural.