Using Drush without local copy of Drupal, only calling site aliases - No site aliases found
If your Drush 9 alias file is remoteproject.site.yml, and it has keys like live:, then your alias should be @remoteproject.live.

If you have multiple remote sites, do not put them in the same .yml file in Drush 9. Make one file per site, e.g. remotesite1.site.yml, remotesite2.site.yml and so on.

Use ./vendor/bin/drush sa to see the list of aliases found by Drush.