The system you are trying to install is more designed for multi room where each unit can play through mopidy and through snapclients. If you are only trying to play through snapclients you are over complicating the setup.
As I’ve said above install mopidy and use /etc/mopidy/mopidy.conf for all the conf files, run as a service (or not but then use the other location for conf files) install snap server and client and it will work, install the android apk on the sticks and on phone and it will work.
I’ve set up multiroom audio using Mopidy, Snapcast and HASS 8 times for various friends and family and the beauty of it is it just works straight out of the box each time.
Currently I have 4 pi’s they can all play the same sent via snapserver, or they can play, using mopidy, Spotify, Tunein or local files. I use either Iris or Musicbox webclient to control them.