I haven’t heard back, so I’m going to take a guess at what you’re trying to accomplish.
You can take the code you already have in place, based on your other post from yesterday:
<div id="page-list">
<?php wp_list_pages('child_of=9& exclude=539,540 title_li='); ?>
</div>
Then wrap it in a conditional statement that checks to see if you are currently on that page or one of it’s children. An example that may work would be:
<?php is_page(array(42,'Murmelins-Parent-page','Murmelin's Parent Page')){
; ?>
Then insert your list pages query, and close out the conditional statement with:
`<?php } ?>
I haven’t tested this code, but in theory it accomplishes what I understand your goal to be. If this doesn’t work, post back a link to your site and some more details and we’ll see if we can help.