issuem-coauthors.php

<?php


function zeen_override_byline($orig_author, $post_ID) {

    $authors = ''; /* get the coauthors */

    if ( function_exists( 'get_coauthors' ) ) {
        $coauthors = get_coauthors($post_ID); /* if no coauthors then just user the original author */
    } else {
        $coauthors = array();
    }

    if ( count($coauthors) == 0 ) {
        $author_id = get_post_field('post_author', $post_ID);
        $authors = '<a href="' . get_author_posts_url($author_id ) . '" title="View all posts by ' . $orig_author . '">' . $orig_author . '</a>';
    } else {
        foreach( $coauthors as $coauthor ) {
            $authors .= ((strlen($authors) > 0) ? '&nbsp;,&nbsp;' : '') . '<a href="' . get_author_posts_url( $coauthor->ID ) . '" title="View all posts by ' . $coauthor->display_name . '">' . $coauthor->display_name . '</a>';
        }
    }

    return $authors;
}

add_filter( 'issuem_author_name', 'zeen_override_byline', 999, 2 );