Are you using the S1 (gray) SONOS controller?

You would need to connect a new (or reset) S2 App on your controller device to your Son’s Sonos system, that’s when the controller device is operating on the same network subnet. To have any system control though, you would require your Sons permission and account login credentials, but for general playback you will be fine without those. You may find it easier though to just use your Son’s Sonos controller device instead.

When a single controller device is operating two ‘separate’ S2 Sonos systems on the same subnet it can sometimes cause an issue as to which Sonos system the controller finds - but there are options to forget a system, as detailed in this Sonos Support link:

https://support.sonos.com/en-us/article/forget-a-system-from-the-sonos-app

My own personal thoughts are to use separate controller devices for each system if they are on the same network subnet.

I was using the gray controller for a system composed of gen 1&2.  My son set up our Move2 to surprise me but w a new email.
 

I can use the email he set up, no problem.

This question originally started after chatting w Sonos. I logged onto chat w my email.  She was helping me reboot an old playbase and didn’t see our new system.  (Sonos Chat was very helpful!)

i also have a system 2 set up at a second home.  It’s gold/gen 2.  Going forward I will use two emails.

Thanks for the help community!

See my response.  Thanks for weighing in. 

Thanks for your thoughts and expertise!!