You could create a shortcode to use in the Page Header content:
add_shortcode( 'author_plus', 'tu_coauthors_plus_shortcode' );
function tu_coauthors_plus_shortcode() {
return sprintf( ' <span class="byline">%1$s</span>',
function_exists( 'coauthors_posts_links' ) ? coauthors_posts_links( null, null, null, null, false ) : ''
);
}
Then you can use this in the Page Header content: [author_plus]
As for the other question, you’ll likely need to check with the developers of Starbox.