Buy an airport express and use that as the input into your Sonos system. Airplay will display the airport express. Then you control the number of Sonos speakers from the Sonos app. The 'how to' set up is on the Sonos support site.
When I stream a Spotify track to my grouped Play and Connect, I can control both Sonos devices. But when I want to stream two different songs to my Play and Connect, ons stream is stopped. The message Spotify goves me is that I can't stream to multiple devices.
No you can't. You have Sonos app for that. Link you spotify account to Sonos IN THE SONOS APP. Then you'll see all your spotify playlists in the Sonos app. You can even search Spotify from within Sonos.
Incidentally you can't be logged online to spotify on more than one device at the same time - so if you are online on your laptop on spotify then shut it down before trying to use it on Sonos - same goes for other mobile phones