DaanL,
You’re not doing anything wrong here, the adjustment of the volume, as far as the current Google integration on Sonos, works the same as the speaker hardware volume buttons, when in a group situation. The feature to adjust the group volume has been submitted for consideration by me and others, but Google/Sonos do not usually announce their development path, or give dates etc.

I understand the Amazon Alexa integration, which started a year, or so, before the Google integration, does have group volume control, so hopefully Google will follow suit. It’s a case of waiting to see what each new update will bring.

Hope that answers your post?

It does, thank you. Although I am surprised that such a basic function is not implemented yet. 

Thanks

Yes, you have to adjust each room-volume in a group by including each separate ‘room-name’ within the voice instructions ..let’s hope the matter gets sorted in the not too distant future.

HI @DaanL.

Welcome to the Sonos community and thanks for reaching out to us.

I would like to agree with @Ken_Griffiths. This is a feature limitation between the integration of Google Assistant with Sonos. However, I would be morethan happy to send this to our engineering department to take a look at and see if they can have this addressed on our end. 

Just to set your expectation, I would recommend subscribing to this topic and the Announcement thread to be updated about any feature release as it may or may not contain your feature request.

Please let me know if you still have further questions or concerns. We are always here to help out.

Thanks,