You can us a Port to send audio to the LG speakers if there is a digital or RCA in. Then you can group them with your Sonos speakers. They may sound vastly different, especially after using  Trueplay to EQ the Sonos speakers.

My LG speakers subwoofer and sound bar are all LG and they’re connected to my TV. How do I hook my speakers to my TV as well? I have Sonos SL one.

I see… You cant with a One SL, unless the LG soundbar has RCA out. Then you can add a Port and group it to the One SL. There will be a delay between the LG and the One. But if its in a different room, the delay will not be that bad.