Do you want to “group” them as meant in https://support.sonos.com/en-us/article/group-and-ungroup-rooms? Or do you want to “bond” them to the Beam as rear speakers as meant in https://support.sonos.com/en-us/article/add-surround-speakers-to-a-sonos-home-theater

To bond them the SL’s must not form a stereo pair, so unpair them first.

Thx for the quick reply . I want to ‘bond’ them - but it I couldn't even set them up as a stereo pair to begin with ; they were not recognized as such. Essentially they are a separate entity as ‘living room 2’, where my beam and sub are ‘living room 1 “ . I tried to follow the article above but did not get any resolution;  the options were not available for some reason ..when I try to add product, it states “two compatible Sonos speakers are required to add surrounds “

Have you first gone to ‘living room 2’ and separated the stereo pair?

There was never s stereo pair to begin with - when I tried to establish that, the response was ‘ you must use a two compatible Sonos speakers to form  a pair …...”   Both separate Sonos systems, (living room 1 and 2) ,as they are now, are connected to the same wifi network as well, so I'm stumped.

Are you sure they are both the same model?  Sonos Ones closely resemble the previous Play:1 models.  The only difference being the Play:1s have physical buttons on top, whereas the Ones have touch sensitive virtual buttons.

Yes, they are both Sonos SL 1 , with the button on the back. I factory reset both, and tried again with same result. The app finds them no problem, but wants to add them as a new room - when I try to force the app to add to the existing Beam setup, that’s when suddenly it doesn't recognize them….odd.

You actually need to add them as separate rooms first.  After they both are added (don't worry about the room names, they will go away once you add them as surrounds to the Beam), then go into the Settings for the Beam and choose to add surrounds.  Follow the prompts to add as surrounds.

Thanx ! It worked ! Now I just need to get their volume set…..

Settings/System/living room/Surround Audio will give you volume controls for the rear speakers.