<?php
/* Untermenü Seitenleiste
 * http://codex.wordpress.org/Function_Reference/wp_list_pages#List_whole_subpages
 */
if (!is_search() && !is_404()) :

  $ancestor_title = get_the_title($post->post_ancestor);

  if(!$post->post_parent){
    // will display the subpages of this top level page
    $children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0&sort_column=post_title"); // sort_column: post_title = ABC, menu_order = wp-admin
  } else {
    // diplays only the subpages of parent level
    $children = wp_list_pages("title_li=&child_of=".$post->post_parent."&echo=0");
    if($post->ancestors) {
      // now you can get the the top ID of this page
      // wp is putting the ids DESC, thats why the top level ID is the last one
      $ancestors = end($post->ancestors);
      $children = wp_list_pages("title_li=&child_of=".$ancestors."&echo=0&sort_column=post_title");
      // you will always get the whole subpages list
    }
  }
  if ($children) { ?>
<div class="ym-grid">
  <div class="ym-gbox">
    <h6 class="ym-vtitle"><?php echo $ancestor_title; ?></h6>
    <ul class="ym-vlist ym-clearfix">
      <?php echo $children; ?>
    </ul>
  </div>
</div>
<?php
  }
endif; ?>

<?php
/* Untermenü Seitenleiste
 * http://codex.wordpress.org/Function_Reference/wp_list_pages#List_whole_subpages
 */
if (!is_search() && !is_404()) :

  if (!$post->post_parent) {
    $ancestor_title = get_post($post);
    $ancestor_title = $ancestor_title->post_title;
  }

  if ($post->ancestors) {
    $ancestor_title = $post->ancestors;
    $ancestor_title = end($ancestor_title);
    $ancestor_title = get_the_title( $ancestor_title );
    #debugVar($ancestor_title);
  }

  if (!$post->post_parent){
    // will display the subpages of this top level page
    $args = array(
      'title_li'     => '',
      'child_of'     => $post->ID,
      'echo'         => 0,
      'sort_column'  => 'post_title'
    );
    $children = wp_list_pages($args);
  } else {
    $ancestors = get_post_ancestors( $post->ID );
    #debugVar($ancestors);
    /*
    debugVar($post);
    $ancestors2 = $post->ancestors;
    debugVar($ancestors2);
    */
    $ancestors = end($ancestors);
    $args = array(
      'title_li'     => '',
      'child_of'     => $ancestors,
      'echo'         => 0,
      'sort_column'  => 'post_title'
    );
    $children = wp_list_pages($args);
  }
  if ($children) { ?>
<div class="ym-grid">
  <div class="ym-gbox">
    <h6 class="ym-vtitle"><?php echo $ancestor_title; ?></h6>
    <ul class="ym-vlist ym-clearfix">
      <?php echo $children; ?>
    </ul>
  </div>
</div>
<?php
  }
endif; ?>