HomePod control
I know that HomePod currently only supports a single appleid, but could another user be signed in on the MacBook and just use the media buttons to control it?
See if this article is of help
https://support.apple.com/en-ca/HT208341
You can “allow speaker access” to anyone, or people on the same network or only people sharing this home. That is set up through the home app by tapping the home icon in top left corner.
Aside from that, anyone can ask HomePod anything while in your home, since it doesn’t have voice recognition.