Two Sonos Play in stereo mode connected with tv via usb-c/aux adapter

I wouldn’t expect them to. Most TV’s don’t output a stereo signal via USB. And even if it did, you’d need to deal with the delay on the input, which would make synch between the audio and video difficult, if not impossible. 

You could use one of the TV's outputs, converted to analog stereo and a 3.5 mm audio plug.

Connect that to the Sonos audio input converter and your Era.

You would still have the echo/delay issue.

But will it still work in stereo mode and transmit audio from the TV? 

I have two EarFun UBOOM L Bluetooth speakers. They are paired in stereo, and one of them is connected to the TV via a 3.5 mm AUX cable, and everything plays in stereo. I’m wondering if two Sonos Play speakers would work in a similar way.

You would need to use the SONOS input converter connected to your 3.5mm AUX cable. This would result in stereo output from a pair of PLAY’s, however, the audio delay causes lip sync issues that will annoy most TV viewers.