You can group the two speakers to the Beam in the Sonos app but make sure Ungroup on Autoplay is disabled so the speakers will stay grouped after the Beam detects an audio signal from the TV. But don’t expect the speakers to stay grouped for an extended period of time especially if they have been idle for a while. Also you may experience a slight audio delay from the grouped speakers when listening to TV audio.

A true surround setup would be to either purchase another One (or One SL) or another SYMFONISK speaker so you can add the pair of same model as actual surround speakers rather than just grouping them together. With this setup, the speakers will always remain “bonded” to the Beam.

If you were to get another speaker of the same/similar type, then you can ‘bond’ them to your Beam. So as an example, you could get another Sonos One/One SL and add/bond the ‘Ones’ to become its HT surrounds. See this LINK

That's not surround sound, it's just a few speakers playing the same thing. In true surround sound, each speaker plays distinct separate channels to add directional cues and ambiance to the overall sound.  For surround sound, you need to bond two same model speakers and/or a Sub with your Beam.