Thanks for your patience @noris, I’ve been playing around a bit and still couldn’t get it to work. But now I do!
So the problem here comes from the ‘homepod’ setup, apparantly changing the settings to match the solution to this problem:
https://community.roonlabs.com/t/homepod-appears-but-no-output/74179/21
Also made it so that the sonos speakers in the kitchen now work through airplay too, and creating a group through airplay is now also enabled.
It’s curious that the ‘allow speaker access’ in the home setup is also attached to the sonos’, but not to the receiver end. Could be that the receiver doesn’t do the check if a device is allowed to use it or not, anyway.
Thanks for your patience Noris, hopefully this response will also help others with a google wifi / airplay combination setup!