If you can’t get an ethernet cable to one of the devices, could you try a low cost plug in wi-fi extender? 

Sorry I was probably not that correct in my explanation. I mean I want to be able to start/stop music and remotely control my systemwhen I am not at home.

You’d need a VPN, and moreover a VPN which was able to handle multicast traffic. 

Opening ports on a router, apart from being a security hole, wouldn’t work. Sonos devices block connections forwarded from the outside.

If you have the Sonos App on a PC in your home, you could use Teamviewer or a similar remote PC access app on your phone, to control the Sonos on the PC remotely from your phone. 

I have just tried this using my own Teamviewer setup and it does work 

When I installed Teamviewer, I didn’t need to open up any port on the router or change any other router settings.