how to display all images from their siblings/ from same parent?

Nice to see Liverpool at the top there!

I’d go about this using a page template. Given that as far as I’m aware we only know the page names I’ll add it in that way.

The process is this:

1. Loop through top level pages
2. Collect child pages as array
3. Loop through child pages

4. Loop through child attachments

   <?php
   
   /*
   Template Name: All images
   */
   
   get_header();
   
   // pages to loop through
   $sports = array( 'Hockey', 'Football' );
   
   // empty array where we collect teams
   $teams = array();
   
   // collect teams
   foreach( $sports as $sport ) {
   
       $page = get_page_by_title( $sport );
   
       $teams = array_merge(
                   get_children( array(
                       'post_parent' => $page->ID,
                       'numberposts' => -1,
                       'post_type' => 'page'
                   ) ),
                   $teams
               );
   
   }
   
   // you could do some custom sorting or randomisation of the order here
   
   // loop through teams
   foreach( $teams as &$team ) {
   
       // get image attachments for each team
       $images = get_children( array(
               'post_parent' => $team->ID,
               'numberposts' => -1,
               'post_type' => 'attachment',
               'post_mime_type' => 'image'
               ) );
   
       // output images
       foreach( $image as &$image ) {
   
           // link to team page
           echo '<a href="' . get_permalink( $team->ID ) . '">';
           echo wp_get_attachment_image( $image->ID, 'medium' );
           echo '</a>';
   
       }
   
   }
   
   get_sidebar();
   
   get_footer();
   

You’ll want to modify the markup a bit and bear in mind this will be quite slow so you may want to consider a caching plugin.