I work IT and trust me, Windows 10 is a piece of work. I'll help you though. You'll want to share the printer over the network. Try this guide. It will work for Windows 7 and 10. But for Windows 7 you need to go to the Devices and Printers window.

https://www.isumsoft.com/windows-10/share-and-connect-printer-over-network.html

For file sharing, the steps are pretty much the same. After sharing a folder just navigate to \\hostname\\sharename to access it or map it as a network drive on your Windows 10 PC. You can also get to the root of the C drive by typing \\hostname\\C$ to use the default admin share on the PC.

This is normal. You will need to enter the login credentials for an admin user account of the target PC you are trying to access. This prevents anyone on the network from accessing shared folders on the target PC without knowing the admin account's user name and password. It's the same password you type when logging in to the target PC after booting it up.

The printer is from 1999 and because of that is not network capable. It probably uses an LPT port.

That's not very practical in this case now that we know it's USB. My post was making an assumption until we knew for sure.

You can configure the other PCs to log in automatically but you probably need to get into the registry. Either that or enable the administrator account you can use to authenticate to the PCs with, and keep the normal user account for your wife to use without a password.

Sure thing! To explain, when you install Windows there is a factory default administrator account that is disabled. This is present at all times so you cannot get locked out of the machine. It's disabled by default, so you normally never see it.