The base unit of the Deco mesh is a router.
There is no Sonos 1, there is a Sonos PLAY:1 and a Sonos One.
Try unplugging all three speakers from power, and then reboot your Deco. Give the Deco 2 minutes to fully come back up, then plug one of your Sonos speakers into it with an Ethernet cable. Make sure your controller device is connecting to the Deco mesh (probably safer for testing to leave any satellites unplugged, one issue at a time). Plug back in to power all three Sonos speakers, and give them a couple of minutes to reboot, and connect. Open the controller, and do some testing.
You could also call Sonos Support directly to discuss it.
When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.
The base unit of the Deco mesh can be configured as a router, but also as an access point. It only should be set up as a router if your ISP “modem” is in bridge mode. With two routers in a set up, devices can get confused. Can you clarify your set up?