Combine with Smart Archives for Multiple authors?

I’m trying to combine coauthors and the smart archives reloaded plugin but can’t make multiple authors show up,

This is the code on Smart Archives that I believe pulls the author that I need to edit but nothing seems to work, any tips?

protected function substitute_author( $post ) {
return get_user_option( 'display_name', $post->post_author );
}

Thanks!

https://www.ads-software.com/plugins/co-authors-plus/