You can group all four speakers together in the Sonos app to play the same music on all four speakers at the same time.

Read more about grouping and ungrouping speakers here:
https://support.sonos.com/s/article/3391?language=en_US

You can also pair two One SL speakers together as a stereo pair:
https://support.sonos.com/s/article/1066?language=en_US

You can add two of the One SLs as surround speakers to the Arc in a home theater setup:
https://support.sonos.com/s/article/2927?language=en_US

You can bond 2 Sonos Ones as a stereo pair, making them a room.  Each speaker can also be setup as a room by itself.  Each room can play it’s own audio or be grouped with other rooms to play in sync for music.

For home theatre, you can bond 2 Sonos Ones as rear surround speakers.  The other two speakers would need to be a separate room(s).  When you group a HT theatre room with other rooms playing TV audio, the HT through will play immediately to be in sync with the video, while the other grouped rooms will be slightly delayed...creating an undesirable echo effect if they are the same  physical space.

I really appreciate your time to answer my questions. They are very helpful and detalled, thanksa million and this was a very nice welcome to the group.