Can multiple authors be assigned on a single custom post?

I have custom post types that I would like to make editable by several users. I created one custom post type using the Toolset plugin. wp_update_post only allows us to set single author:

$user_id = array();
$userIds = get_field("agency_to_author",$_POST['post_ID']); // Get Multiple User assing using acf field.
foreach ($userIds as $key => $value) {
     $user_id[] = $value['ID'];
}
if(!empty($user_id)){
     $arg = array(
         'ID' => $_POST['post_ID'],
         'post_author' => $user_id,
     );
     wp_update_post( $arg );    
}