How to define alias dependent Drush extensions?
Instead of installing the drush extensions in a user specific scope within your user's profile, you can install them on a per-project (Drupal instance) base in your {PROJECT_ROOT}/drush folder.

Drush 9 checks for the existence of a drush folder one level above the Drupal web root.

This is easiest to manage by utilizing Composer for dependency management and adding a Drush installer path, Drush and any Drush extensions to the composer.json file. But of course you can also setup everything by hand.