To get a Sonos device to add to the system that has a line in, and connect the pre-amped turntable to that. Currently, the line in on your Era 300s are turned off, as they’re being used for surrounds. 

@CNM

I suppose the devices you listed are set up as a surround system. In this configuration the Era300 speakers analouge line in function is disabled. 
Best way for phono playback would be another device with an analogue input option. This could be an Era100 or another Era300, each with the Sonos line in adapter, or a Sonos Five, Port or Amp. 
An older S2 Connect or Connect Amp also would work, but I recommend using a newer device with better hardware. 
Then imho you won’t be running into any problems. 
EDIT:

was writing at the same time as @Airgetlam did

If I add 1 era 100 and turntable to the same system above will the records play through all the speakers or just the era100? Also when watching a movie with the sound also come out of the era100?

Yes. You could group the Era “room” with the home cinema “room” or choose line in as a source in the “home cinema room” to play records. If you do not need a speaker with the turntable, the Port is also an option (more expensive than an Era 100 with adapter though).