Separate user bases or hide users of another role or connected to another minisite

You can use a subdomain for every site. Then it’s easy to separate the users per wp-config.php:

$base = str_replace( '.', '_', filter_input( INPUT_SERVER, , 'SERVER_NAME' );

const CUSTOM_USER_TABLE $base . '_users';
const CUSTOM_USER_META_TABLE  . '_usermeta';

unset($base); // clean up