@1ee
As far as I know that won’t work, because Alexa and Sonos Voice Control and probably Google Assistant too do not support multiple Music Services or Accounts of one Service as standard service. There imo due to technical reasons just can be one account as standard for the voice assistant. You just can use also other music services next to the standard one by adding their name at the end of your voice command. But you can’t add multiple accounts of one service to Alexa & Co.
I don’t know if anything’s changed in 4 years but if not then it’s not possible immediately(*. In this thread there’s a workaround by separating certain Sonos speakers to their own network and associating Amazon/Spotify to that. And then putting the rest of the speakers on another similarly. I don’t know how convenient that would in effect be especially now that the current app still struggles using/switching between multiple systems. (And if all's working ok I wouldn’t tempt fate by factory resetting etc.)
I suspect you use Alexa via amazon’s devices or on older Sonos devices(?)
I understood that you have two separate Spotify accounts showing up in the Sonos app music services(?)
If your Sonos device supports Sonos Voice Control, could one workaround be to add that and then associate your wife’s Spotify account to that as preferred service? Then you’d use “Hey Sonos, play …” when wanting to play through your wife’s account, and “Alexa, ...” when yours.
I realise it’s not ideal but could that set up work?
I nowadays use Sonos Voice Control more instead of Alexa. (Only use Alexa when I want to start certain Sonos Radio station because Sonos Voice Control plays the wrong one.)
https://support.sonos.com/fi-fi/article/list-of-voice-requests-for-sonos-voice-control
https://support.sonos.com/en-us/article/control-sonos-with-sonos-voice-control
*) Edit:
From the below article:
“Alexa doesn’t let you do that, but it should be possible for you to create multiple Alexa profiles within an Amazon Household and have every individual Alexa profile linked with the corresponding Spotify account. You will then have to remember to switch Alexa profiles when using voice commands to avoid interrupting each other’s playback.”
https://community.spotify.com/t5/Android/Playing-spotify-on-sonos-and-alexa-from-different-phones-logged/td-p/5628357