page siblings navi

first part - into functions.php

function siblings($link) {
    global $post;
    $siblings = get_pages('child_of='.$post->post_parent.'&parent='.$post->post_parent);
    foreach ($siblings as $key=>$sibling){
        if ($post->ID == $sibling->ID){
            $ID = $key;
        }
    }
$number = count($siblings);
$before_url = ($ID == 0) ? '' : get_permalink($siblings[$ID-1]->ID);
$after_url = ($ID == $number-1) ? '' : get_permalink($siblings[$ID+1]->ID);

    $closest = array('before'=>$before_url,'after'=>$after_url,'current'=>$ID+1,'total'=>$number);

    if ($link == 'before' || $link == 'after') { echo $closest[$link]; } else { return $closest; }
}

second part - for page.php

<?php $siblings = siblings(''); if( $siblings ) : ?>
<?php if( $siblings['before'] ) { ?>
<a href="<?php echo $siblings['before']; ?>">Previous </a>
<?php } else {
echo 'Previous '; } ?>
<?php echo $siblings['current'].'/'.$siblings['total']; ?>
<?php if( $siblings['after'] ) { ?>
<a href="<?php siblings('after'); ?>"> Next</a>
<?php } else { echo ' Next'; }
endif;?>