How to add the sort the output order of these pages?

I’m working with code that’s new to me and I cannot figure out how to add the argument to sort this asc. Can anyone explain how I would add that argument to this example?

<?php global $post;
$parent = $post->post_parent;
if( $parent ) :
    $siblings = get_pages( 'child_of=' . $parent . '&parent=' . $parent . '&exclude='
. $post->ID);
    if( $siblings ) foreach( $siblings as $sibling ) :
        echo '<div id="featured">'.get_the_post_thumbnail($sibling->ID,'side', array ('class' => 'alignthumb'));
        echo '<a class="sidethumb" href="'. get_page_link( $sibling ->ID ) . '">' . $sibling->post_title. '</a></div>';
    endforeach;
endif;
?>