By default, the front-end audience selector will show audiences used by events in the current group/view.

You can override this to show specific audiences on a per-group basis by adding this to your public.config.php file.

$_LW->CONFIG['CALENDAR_GROUP_CATEGORIES_AUDIENCE']=[ // custom audience types to display on group calendar(s)
        // Group ID => Array of audiences
        1 => ['Audience 1', 'Audience 2'] 
];