Editing function in WordPress template - can edit just one variable?

I know pretty much no PHP other than what I've tinkered with on WordPress, but I'm trying to customize my theme to allow two authors to be listed on the front-end of posts.

I installed the Co-Authors Plus plugin (Here) And from the back end it's working well, both authors show up.

For it to show up on the front end, according to several support articles I need to adjust the theme functions to check if there are multiple authors, and if so display them.

I understand the basics and identified the theme file, but have no idea how to incorporate it because it seems that the theme isn't calling a function to display the authors, it's calling a variable in a much larger function (again, I don't know php, so if I'm wrong here, please let me know).

This is the bare bones code provided by Co-Authors Plus:

if ( function_exists( 'coauthors_posts_links' ) ) {
coauthors_posts_links();
} else {
the_author_posts_link();
}

But when I look in the functions file I don't see where that could go. I see this:

// mom_post_meta
function mom_posts_meta ($class = '', $display = null) {
    $num_comments = get_comments_number(); // get_comments_number returns only a numeric value

if ( comments_open() ) {
    if ( $num_comments == 0 ) {
        $comments = __('No Comments', 'theme');
    } elseif ( $num_comments > 1 ) {
        $comments = $num_comments .' '. __(' Comments', 'theme');
    } else {
        $comments = __('1 Comment', 'theme');
    }
    $write_comments = '<a href="' . get_comments_link() .'">'. $comments.'</a>';
} else {
    //$write_comments =  __('Comments off', 'theme');
    $write_comments = '';
}
$author_link = esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) );
if (class_exists('userpro_api')) {
    global $userpro;
$author_link = $userpro->permalink(get_the_author_meta( 'ID' ));
}

$categories = get_the_category();
$separator = ', ';
$cats = '';
if($categories){
    foreach($categories as $category) {
        $cats.= '<a href="'.get_category_link( $category->term_id ).'" title="' . esc_attr( sprintf( __( "View all posts in %s", 'theme' ), $category->name ) ) . '">'.$category->cat_name.'</a>'.$separator;
    }
}
    $output = '<div class="mom-post-meta '.$class.'">';
    $author = mom_option('post_meta-author') == 1 ? '<span class="author vcard">'.__('Posted by:', 'theme').' <span class="fn"><a href="'.$author_link.'">'.get_the_author().'</a></span></span>': '';
    $date = mom_option('post_meta-date') == 1 ? '<span>'.__('On:', 'theme').' <time datetime="'.get_the_time('c').'" itemprop="datePublished" class="updated">'.get_mom_date_format().'</time></span>': '';
    //$date = mom_option('post_meta-date') == 1 ? '<span>'.__('The last Update:', 'theme').' <time datetime="'.get_the_time('c').'" itemprop="datePublished" class="updated">'. get_post_modified_time(mom_option('date_format')).'</time></span>': '';
    $cat = mom_option('post_meta-cat') == 1 ? '<span>'.__('In', 'theme').': '.trim($cats, $separator).'</span>': '';
    $comments = mom_option('post_meta-comments') == 1 ? '<span>'.$write_comments.'</span>': '';
    if ($display == 'date_comments') {
        $output .= $date.$comments;
    } else {
        $output .= $author.$date.$cat.$comments;
    }
    if(function_exists('the_views')) {
        $output .= '<span>'.__('Views:', 'theme').' '.the_views(false).'</span>';
    }
    $output .= get_mom_show_review_score();
    $output .= '</div>';
    echo $output;
}

I see that the $author line is what defines the output on the front end, but without an understanding of php I'm not sure how to include an if-else statement in there. I tried a few amateur edits, and just got errors. Any guidance of how to incorporate this while preserving the theme styling would be so very much appreciated.

I'm using Momizat's Goodnews theme.