Not currently, no. I suppose if you were to set up a VPN, it might work, as the controller needs to be on the same network as the Sonos. Or, I think Spotify Connect works remotely if it is still connected via the Spotify system, not through the Sonos system.

When I'm at home the only system that shows up is our home system. No way to access the beach house system

What are you trying to achieve? Is the system in your beach house still play and you want it to stop playing? Or do you want to physically turn it off? Because Sonos is meant to be always on, so you can’t even turn off the system in your home. You can stop it from playing, but that’s something else.

If you want to really turn the system in your beach house off (to preserve electricity or for safety reasons) you could look at using connected plugs. I use Osram and Phillips Hue plugs to control some of the lights in my home. These can be controlled from my phone wherever I am. When powered down your system will not receive any updates and it will take some time powering up again. Sometimes it will need to be updated immediately after powering up - especially if the Sonos app has been updated.

No not completely off, I just wanted to be able to stop the music if it gets left on and we aren't there.

If you’re going to be absent for days or weeks at a time, power the system down. Why heat the planet any more than it is already.

there are several ways to turn on/off  your Sonos system remotely. 

Not within the Sonos software. There are a multitude of third party solutions to control power to devices in your home. Sonos does not provide that option in its own software.