One Sonos account, no need for more. Add several Spotify accounts to that Sonos account. Just download the app onto your phone, connect to existing system and add your Spotify account.
It's your wife's Spotify at the moment because that is what has been added, not because the Sonos account uses her details.
Thanks for the advice John. So if we have guests over who would like to play from their phone, do we have to do the same thing, there’s no way they would be able to sign in with their own spotify account and play?
In the case of Spotify there is Spotify Connect, which allows users to play directly from the Spotify app. Of course, you would have to allow them onto your home WiFi. Sonos speakers are Spotify Connect compliant.
You can use Spotify Connect yourself, for that matter. Some users prefer to use the Spotify app, rather than the integration of Spotify into Sonos.
https://support.sonos.com/s/article/1153?language=en_US