You are welcome to read, search, download, copy, print, or give away any of it. You're certainly free to incorporate portions of these books in what you create, and sell that. That's the nature of the creative process.
Created stuff is meant to be shared.
That s why the creative person created it. Well, maybe someone wrote that. I just made it up, but it sounds as though someone else might have written it earlier. It got said, and it fit what I wanted to say, so I said it. Creativity stimulates the creators and entertains everybody else.