how to display sub sub level pages

Hi.

I am trying to create a dynamic menu that I can show all related child pages but i have run into a small problem. the current system will show all children when on a top level page and a sub page, however, when I am on a page 3 levels deep (sub sub page) I can only display the pages related to the sub sub page. I just need to show level 2 and any related children.

example:
Top level
– sub page
– – sub sub page

here is the code i am using in my template this far:

<?php
if($post->post_parent)
$children = wp_list_pages(“title_li=&child_of=”.$post->post_parent.”&echo=0″);
elseif ($post->post_parent->post_parent)
$children = ‘test’;
else
$children = wp_list_pages(“title_li=&child_of=”.$post->ID.”&echo=0″);

if ($children) { ?>

<?php echo $children; ?>

<?php } ?>