SOLVED
If anyone wanna use the same code i used/editted.
<?php
$children = wp_list_pages('title_li=&child_of='.$post->ID.'&echo=0&depth=1');
if ($children) { ?>
<ul>
<?php echo $children; ?>
</ul>
<?php }
else {
$children2 = wp_list_pages("title_li=&child_of=".$post->post_parent."&echo=0&depth=1");
} ?>
<ul>
<?php echo $children2; ?>
</ul>
if statement: Shows the childeren of a page and if end page doesnt have childeren.
Else: Show it from the last parent.
