This was the best advice for me. The link shows the difference between Home Sharing and Music Sharing which allows you to play music from another computer, simply by enabling Music Sharing from both computers - the link shows how to do it for Mac and for Windows.
Home Sharing allows you to move music between libraries via drag and drop. But to your point, the same AppleID and Password needs to be entered into all computers on the network. Also, it seems to be omni-directional - using my wife's AppleID/Password allowed copying in either direction. Works great. Thanks for the tip.
A copy of the link: iTunes: How to share music and video