Phew! I almost gave up on this...
The books are made in Adobe InDesign and the program includes a "Publish Online" feature that hosts the books on Adobe servers for you. Several of you commented that QR codes appeared to not be working or would only work if you hovered your mouse over one specific spot on the code. Went back and forth with customer support with very little help.
But I found a solution! It's possible to create pdfs with "interactive elements" including links! So those are now uploaded and hosted directly from the site and the links should be working much better! (Only book I'm still having a hard time with is the mallet book) They should also be alot easier to print.
There's now also an option to download all the books at once as a .zip file.
Thanks again to everyone testing these books for me. Keep those comments coming!