Hi @AndreaBoerio, welcome to the Sonos Community!
I’m sorry to hear that you’re having issues with Spotify on your system.
For your first issue, Spotify has a stream limitation where each Spotify account can only be played at a single IP address at any given time. Either you play from Sonos, from your phone, from your computer, but not all at once. You can have concurrent streams within the same Sonos household when using the Sonos app (for example; one album on a Sonos One, and another album on a Sonos Five), but if you use a different non-Sonos device, then Spotify will stop playing to Sonos.
Regarding the second issue, since playing from the Spotify doesn’t play ads, then reauthorizing the account in the Sonos app may resolve this. You can do this by opening the Sonos app and tapping on the account icon, then going to Content Services → Spotify → User 2’s account → Reauthorize Account. After doing this, try playing through the Sonos app again to see if you still receive ads. If so, then please reach out to our support team for further troubleshooting.
I hope this helps!