function pm_toolset_related_posts_fields($default_uri, $native_slug, $post, $slug, $native_uri) {
    global $wpdb;

    // Do not change native permalinks or differnt post types
    if($native_uri) { return $default_uri; }

    // List of relationship fields that should be replaced
    $relationship_fields = array(
        'custom-post-1', // Use %__custom-post-1% tag in Permastructure settings
        'custom-post-2', // Use %__custom-post-2% tag in Permastructure settings
    );

    foreach($relationship_fields as $field) {
        if(strpos($default_uri, "%__{$field}%") === false) { continue; }

        $relationship = $wpdb->get_row($wpdb->prepare("SELECT parent_id, child_id FROM {$wpdb->prefix}toolset_relationships as r LEFT JOIN {$wpdb->prefix}toolset_associations AS a ON r.id = a.relationship_id  WHERE slug = %s", $field));

        if(!empty($relationship->parent_id)) {
            $related_post_id = ($post->ID !== $relationship->parent_id) ? $relationship->parent_id : $relationship->child_id;
            $related_post = get_post($related_post_id);

            $default_uri = str_replace("%__{$field}%", $related_post->post_name, $default_uri);
        }
    }

    return $default_uri;
}
add_filter('permalink_manager_filter_default_post_uri', 'pm_toolset_related_posts_fields', 10, 5);