Unless I’m mistaken, “eBooks” are electronic versions of the book, like you would read on a Kindle, iPad, etc. The audiobooks are labeled “audiobook” and there are only a few of them (Bones are White, Blood is Red) available from this web site.
Click on the book you want or click “view options” for the book you want. You’ll see a bunch of options. The audiobooks are labeled as [ebooks]. Click the + to add one, then add to cart. Repeat for the others you want and then check out. Hope this helps!