我不完全理解你的问题是什么，主要是因为你在谈论父母和孩子，但这永远不会显示页面的家长，更不用说祖父母了。

我在这里对您的代码进行了注释，以向您展示代码中到底发生了什么。

function wpb_list_child_pages_popup() { 

    // Get the current WP Post object
    global $post;

    /**
     * If post_type of current WP Post object is \'page\'
     * and the post_parent in the WP Post object is set
     */
    if ( is_page() && $post->post_parent )
        /**
         * Get all wordpress pages that are a child of this pages parent.
         * In other words get THIS page and all it\'s siblings
         */
        $childpages = wp_list_pages( \'sort_column=menu_order&title_li=&child_of=\' . $post->post_parent . \'&echo=0\' );
    /**
     * If this page doesn\'t have a parent
     */
    else
        /**
         * Get all wordpress pages that are a child of this page
         */
        $childpages = wp_list_pages( \'sort_column=menu_order&title_li=&child_of=\' . $post->ID . \'&echo=0\' );

    if ( $childpages ) {

        $string = \'<ul id="child-menu">\' . $childpages . \'</ul>\';
    }

    return $string;

}

add_shortcode(\'wpb_childpages_popup\', \'wpb_list_child_pages_popup\');

我猜你只是想要一个包含所有页面的列表，这些页面通过（祖辈）父母、（祖辈）子女或兄弟姐妹“连接”。此函数返回一个包含所有这些内容的字符串，无论您在哪个同级上。

function wpb_list_child_pages_popup() {

    // Get the current WP Post object
    global $post;

    if ( is_page() ) {

        /**
         * Get \'first\' parent, the highest ranking post parent which is the ancestor of all.
         * @var array
         */
        $ancestor = array_reverse( get_post_ancestors( $post->ID ) );
        // If there is no ancestor, set ancestor to this page.
        if ( empty( $ancestor ) ) {
            $ancestor_id = $post->ID;
        }
        else {
            $ancestor_id = $ancestor[0];
        }

        // Get childpages from ancestor
        $pages = wp_list_pages( array(
            \'child_of\'  => $ancestor_id,
            \'title_li\'  => \'\',
            \'echo\'      => 0
        ) );

        $string = \'<ul id="child-menu">\';
        // Ancestor is not included in the $pages so add this manually
        $string .= \'<li class="ancestor"><a href="\' . get_the_permalink( $ancestor_id ) . \'">\' . get_the_title( $ancestor_id ) . \'</a></li>\';
        $string .= \'<ul class="children">\';
        $string .= $pages;
        $string .= \'</ul>\';
        $string .= \'</ul>\';

        return $string;
    }
}
add_shortcode(\'wpb_childpages_popup\', \'wpb_list_child_pages_popup\');