Grouping rooms for simultaneous streaming

What happens if you just cable one Sonos device only direct to your router and uncable all your other Sonos devices… just reboot the ‘other’ (uncabled) speakers for good measure… do they then work?

Ensure the wired Sonos device is positioned at least one metre away from your router so that it’s WiFi AP is no too close to cause any interference. 

You might also check the controller's about section to insure all are on the latest version of the software and firmware. Sometimes the update tool misses updating one or more.

 Are the WiFi radios on each speaker turned off?  The only WiFi radios that should be left on are for soundbars as that is how the soundbars bond to surrounds & sub.

I'd call Sonos support before disabling radios, they rarely recommend that.

Disabled the wireless for 2 of the rooms, the main room has a sub and refused to turn off wireless. Using the main room as a base can stream to one of the additional rooms but not the other. Will checkout the updates & firmware. (It's a simple matter to re-enable the wireless so if that's not the problem I will restore it) 

Ah I don't have a controller, just the App, any ideas where I can check the update/firmware of each speaker? 

The controller is the app. ;) We use it as ‘common’ shorthand, and as a good/fair indicator that all it is is a remote control to see what is happening on the computers in each speaker.

Make sure that WiFi is turned on for all speakers. 

If you click on the gear at the top right of your controller, then click on ‘manage’, which will appear under it, then click on ‘About your system’, you can see the information about each speaker and firmware.

If you don’t click on that, and instead scroll down, you can click on ‘System updates’ to check for updates. Note it checks, but only says if you need to, or don’t, it doesn’t tell you which you’re running there. 

The Sonos app is called a controller. Other controllers are the desktop apps and play.sonos.com (page in desktop mode on mobile).

https://support.sonos.com/en/article/update-your-sonos-speakers
 

 The sub is part of a “bonded” system so should have its radio on.  I have all my Sonos rooms on wireless and they perform flawlessly, but for some reason you say your WiFi does not allow a connection to Sonos gear.  
 
 When some Sonos speakers are using Ethernet they will broadcast the SonosNet WiFi.  From what I read other wireless Sonos speakers will attempt to connect to this SonosNet WiFi network.  Others in this community can better define how this works and whether it could cause connection issues.

 In the app go to Settings (gear icon) - Manage - About Your System.  Scroll down to see your info.  Version should be:  16.4.2 (build 81.1-58074).  All devices should be on this version.

 When you say “all speakers have been assigned IP Addresses via DHCP” do you mean you gave all the Sonos speakers a Reserved IP Address?