Hi @Gc_in_china
Sorry to hear of this issue you are having with your Spotify accounts and Sonos - it is not expected behaviour. You should be able to play one stream from each sub-account at the same time. More than that, if all the destinations are Sonos speakers, you should be able to play multiple streams from a single account.
As a test, could you please try playing from Account 1 on a device that is not a Sonos speaker, then play from Account 2 on another device that is also not Sonos - does the first stop playing, as with your report when using Sonos? If so, I recommend you contact Spotify for assistance.
If, on the other hand, music continues playing, then my recommendation would be to remove all Spotify accounts from your Sonos system. Once they’re all gone, add Account 1 only and test again - if there is an improvement in the behaviour, try adding the other accounts to your Sonos system - only if that’s what you want to do, of course.
Remove a music service account from Sonos
Add a music service to Sonos
I hope this helps.