How to use custom taxonomies to reference complex relationships?

Taxonomies are probably not the best option: There is still no table for term meta data, and if you are using a people custom post type plus a taxonomy of the same name, you will have a hard time keeping everything synchronized.

Install the plugin Posts 2 Posts, register a connection between people and movies:

function connect_people_movies() 
{
    p2p_register_connection_type( 
        array(
            'name' => 'people_movies',
            'from' => 'people',
            'to' => 'movies'
    ) 
    );
}
add_action( 'p2p_init', 'connect_people_movies' );

See the plugin’s wiki for more instructions and examples.