First you will need to get all the music he wants to listen to off the CDs.
Then you will need a music library that is accessible to the Sonos – you can keep the music on the laptop but will need to switch it on or keep it running whenever he wants to listen to music. I don’t use itunes, so can’t say whether Sonos can access it as a music library. I’m sure someone else can.
You may need to get a Sonos Boost if the thickness of the walls causes problems with wifi signal propagation.
Personally, I’d ditch itunes, rip the CDs to a lossless and open format like FLAC and buy a small NAS system ( ideally Synology or Qnap ), but that is maybe overkill and influenced by the fact that I think itunes is the work of the devil.