You should be able to Factory Reset his Sonos and set them up on his account.

I think, but haven't tried, the transfer ownership moves all Sonos. 

Thanks Stanley, 

If nothing else comes through i might give that a go.

Cheers

Andrew

The Transfer System Ownership option will only transfer the connected speakers in that particular app/system to the new account. It will not also transfer every device you have registered on your original account.

Thanks Mr T, 

That’s the way it sounded to me too.

Cheers

Andrew

I used the option last week to transfer some speakers to a different account. The process required a couple of attempts in the new Sonos app but it did successfully complete and register the devices under the new account.