Books 1 to 5 are supplied as both .epub and .mobi files.

You can open the epub files using the Books app on iOS devices.

You can open the .mobi files on Kindle devices or with the Kindle player app, which is free to download and has versions for Android and iOS devices.

Book 6 - Off Piste skiing skills - is supplied as both .epub (Books app in iOS) and .pdf files.

And, there’s a free .epub programme that works well if want to read the .epub files on a PC: Calibre E-book manager.

I hope that helps.

Best regards,

Hugh