Multiple Order by in Wordpress

$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;

if($_GET['auteurs'] != ''){

    $metaSearch[] = array(
        'key' => '_auteurs',
        'value' => $_GET['auteurs'],
        'compare' => 'LIKE'
    );

}

if($_GET['nr_collection'] != ''){

    $metaSearch[] = array(
        'key' => '_nr_collection',
        'value' => $_GET['nr_collection'],
        'compare' => '=='
    );

}

if($_GET['revue'] != ''){

    $metaSearch[] = array(
        'key' => '_tome',
        'value' => $_GET['revue'],
        'compare' => '=='
    );

}

$args = array(
    'post_type' => 'article',
    'posts_per_page' => 20,
    'paged' => $paged,
    'meta_query' => $metaSearch,
    's' => @$_GET['title'],
    'orderby'    => 'meta_value_num',
    'meta_key'   => '_auteurs'
);

$wp_query = new WP_Query($args);