Wordpress navigation for siblings

wp_navi_siblings.php

<?php
/*
* Based on https://gist.github.com/LL782/3551634
*/
function wp_links_siblings($postID = null){
	if(!$postID){
		global $post;
		$postID = $post->ID;
	}
	$ancestors = get_post_ancestors( $postID );
	/* Get the top Level page->ID count base 1, array base 0 so -1 */ 
	$parent = ($ancestors) ? $ancestors[0]: $postID;
	$pagelist = get_pages('child_of='. $parent .'&sort_column=menu_order&sort_order=asc');
	$pages = array();
	foreach ($pagelist as $page) {
		$pages[] += $page->ID;
	}
	$current = array_search(get_the_ID(), $pages);
	$prevID = ( isset($pages[$current-1]) ) ? $pages[$current-1] : '';
	$nextID = ( isset($pages[$current+1]) ) ? $pages[$current+1] : '';
	return [
		'next' => $nextID,
		'prev' => $prevID
	];

}