Mavericks OS can't upgrade, App Store not working

I have a Macbook Pro, Late 2013 that I'm trying to update. It's currently running Mavericks OS X 10.9.5. When I follow links for older OS versions that send me to the App Store, the App Store will not accept the email/password combination that I know is correct (after testing on another device) ("Your Apple ID and password are incorrect"). This computer was owned by someone who is now deceased and their own Apple ID is irretrievable. I've tried creating a bootable USB drive with an OS install, but the drive does not appear in the start up (following steps online). I wiped the computer and reinstalled Mavericks, but still no luck with the App Store.

Does anyone have any advice?