You can play to one speaker and group that with others in the Sonos app. You cannot Airplay to a (named?) Sonos group.

And, the corallary,..you should only stream an AirPlay 2 signal to a single Sonos ‘target’, and let the Sonos system do the grouping with other Sonos ‘rooms’. 

This does pre-suppose that you have a Sonos device that is AirPlay 2 capable. The older speakers are not. For instance, I can send an AirPlay 2 signal to my Sonos Ones, but in order to get the PLAY:1s involved, they must be grouped with the Sonos Ones receiving the AirPlay 2 signal, I can’t ‘send’ to them directly using AirPlay 2. 

Your Arc should be fine for AirPlay 2, @Carolina96 

Send your AP2 music to the Arc, then add your other rooms using group.