Your Google units are  not "signal boosters". They arre a mesh network. 

If you think they are just signal boosters it's no wonder you don't seem to get what's wrong here.

I’m diggin through my very limited Xfinity account settings for wifi and can’t find anything that would allow me to select modem only, or even disable DHCP

Checking settings on both the website and mobile app, nothing so far. 

Please post model number of router

Try enabling bridge mode

https://www.xfinity.com/support/articles/wireless-gateway-enable-disable-bridge-mode

Was finally able to get all 4 devices on the same system by bringing everything upstairs, factory resetting them all, plugging them directly into the modem. 

The two devices staying upstairs seem to be working fine. The other two I unplugged and brought back downstairs are still on the system, but in *Not Connected status. They just won’t connect

I think I might be done 

Bridge mode is modem only mode by a different name.

Just enable bridge mode on your cafinitu router and stop wasting time doing random pointless things!!!

yea, I was able to login to the xfinity admin finally, had to dig for that. The definition of the bridge mode basically said it would turn off all connections aside from the main modem like you mentioned which would have been good for resetting the devices. But I was able to do that thru the factory reset. Now that I have all devices are on the same connection so that they can all be on the same *System, two of them are simply out of range. In other words, I need my signal boosters on and working to use devices downstairs, but unfortunately won’t be manageable through one Sonos system.  One option could be getting on a new phone, setting up a new account/system for downstairs only. Just won’t be able to have a full-home surround system for music. 

Everything you have tried so far has been completely pointless. It's just one router setting. One tap on your mobile. Please don't give up now!!!!

What are you talking about?

Have you enabled bridge mode?

Okay, so enabling Bridge Mode shuts everything down.  Then I reboot everything while it’s down? Do I go back in and turn Bridge Mode off afterwards? 

You need to connect everything to your Google mesh wifi. That is your wifi network now.

You should have a Google wifi network available for your phone to connect to. Do you?. 

You WANT to shut those things down that  it says it will shut down

Alright man, thanks again for all the help. You really should be getting paid for this

Unfortunately I’m giving up for now. I just turned on bridge mode and it shut everything down, couldn’t get anything connected. 

Had to reboot the router, turn bridge mode off and finally got my network back. Had enough of the fam yelling at me for one morning

OK  With bridge mode enables you won't be able to connect anything to your Xamfinity wifi. That is the point. But you should be able to connect your phone and Sonos to your Google mesh wifi.

But I can understand your frustration.  I suggest that if you feel like another go you call Sonos Support to talk you through it.

Good luck

Hi @Arkaeden, putting your Xfinity box into bridge mode is a great idea all around, independent of your Sonos system. As it stands, your Xfinity Wi-Fi is competing/interfering with your Google Mesh Wi-Fi … plus many of your family’s devices are connecting to the weaker/slower Xfinity Wi-Fi.

Granted, moving all your family’s devices off of Xfinity Wi-Fi and onto Google Mesh Wi-Fi is a PITA. But that is a one-time thing. Write down the SSID and password of your Google Mesh Wi-Fi so that every time a device fails to connect to Xfinity Wi-Fi you’ve got all the information at your fingertips. Better still, before you put the Xfinity box into bridge mode make an effort to switch as many devices as you can onto Google Mesh Wi-Fi.

Your home network will be all-around better once you’ve “turned off” Xfinity Wi-Fi.

Thanks again

“Granted, moving all your family’s devices off of Xfinity Wi-Fi and onto Google Mesh Wi-Fi is a PITA.”

This is what made me put on the breaks.. lol. We have at least 50 devices / smart home, etc.

But what i didn’t realize is that Google Mesh and XFinity were two separate things. I like your idea of gradually moving everything over to Mesh first, then turning the bridge on when nobody is home. 

One thing that MAY work and save a lot of hassle.  Enable bridge mode on the Xafinity router.  Change the Google WiFI SSID and paasword to be identical to those of your Xafinity router.  Retire to a safe distance.

Not “things”. Networks.