Work in Post Parent

How do I get url of a thumbnail that belongs to a parent post (one page above the level that I am seeing)?
For the default thumbnail I use:

     <? php if ($ post-> post_parent) {
         $ parent_thumbnail = wp_get_attachment_image_src (get_post_thumbnail_id ($ post-> post_parent), 'thumbnail');>
         <img src = "<php echo $ parent_thumbnail [0];?>" />
         <? php}>

How do I call function kdMultipleFeaturedImages for this case?

http://ww.wp.xz.cn/plugins/multiple-featured-images/