Yeah, I'd definitely recommend getting yourself a code, sooner or later. But you don't need to install via whatever medium (DVD or USB) comes with that code, and in fact it's not a great idea. Using your dad's install, you can get yourself the latest version of Windows 10, as opposed to installing an earlier build and then updating all at once, and potentially missing critical files along the way.
If you buy from Amazon Direct (not Marketplace), the code you receive should be fine, and it will be valid no matter which version of Windows 10 you install. You might have to wait a couple of days for the delivery, but then again you won't need the code itself right away either.
