Correct, you could ‘group’ a third Roam as a second ‘room’ and have it play the same source in sync. It would be in mono, not stereo mode, though. 

very thankful

but would it have to be via bluetooth?

You can’t ‘group’ rooms in Bluetooth. The rooms would need to be grouped in the Sonos controller on Wi-Fi, but the source of the signal wouldn’t matter, for these Roams. 

@Cubi.
See this link below for an explanation of grouping/ungrouping Sonos ‘rooms’ whilst they’re connected to your local WiFi network.

 https://support.sonos.com/en-us/article/group-and-ungroup-rooms

When the rooms/speakers are grouped together, you can choose to play music to that group of speakers over WiFi, via the Sonos App for example, or you can play to ALL using Apple Airplay2, or whilst using a Bluetooth connection to one of the Roams too. When grouped, the audio will play to all.

Gracias, por la informacion

thanks for the information