None of these look free, is their something special I need to do ?
Probably need a Springer account or something along those lines. I'd suggest using scihub (schi-hub (dot) se) to download the books using the links provided in the medium article.
Edit: should be sci-hub (dot) se
A few months back Springer offered all these books plus a lot more for free download. I'm pretty sure I downloaded all of them. Here is a magnet link if you still want them. It's 15.3Gib.