@Mikki4eyes,

Usually the ‘other’ persons Music service is added to the same Sonos Household and they can then use that to listen to their own music, or you can create more than one ‘System’ on the network and each user can user their own speakers.. So just as examples:

My Wife and I have our own Amazon music services, which we have each added to our Sonos System in rooms on the ground floor of our Home.

See this link about how to add multiple music services from the same provider to a Sonos system:

https://support.sonos.com/s/article/3624

Our two children did also once have their own Sonos systems in their bedrooms - and all that is needed in that case is to create a ‘new’ Sonos system and add their own music services to their own personal setup.. this can all be done using the same Sonos Account, or a separate Sonos account. See this link on how to create a new Sonos system:

https://support.sonos.com/s/article/2627

In our case the children both used our Sonos Account, but had their own music services installed. They also used their own mobiles to control their own systems.

Anyhow I hope that information helps to answer the question you are asking here.

Just an addition: you cannot have more than one Sonos account on one system.

If you’re looking for something more temporary, there are 3 other ways that a guest could play their own music on your Sonos system.

1 -  The could physically connect the headphone output of their phone to the aux input of a Five, Port, or Amp (plus some of the older Sonos devices)

2 - If using an Applie iPhone/Tablet, they can sign on to your WiFi network and play audio wirelessly through airplay.  

3 - If you have  Roam, the could play audio via bluetooth to the Roam.  You can then group the Roam with other speakers in your system.