page template for custom post type

I would take advantage of post-type hierarchy, and the single-{cpt}.php template file, to accomplish everything you’re after.

You can use $post->post_parent (recursively) to determine if the current CPT is a parent, child, or grandchild, and also to query content from parent and grand-parent CPTs for output.

CPT Hierarchy

You can create a custom function to determine the hierarchy of the current CPT; e.g.:

function wpse121567_get_cpt_hierarchy() {
    // Make sure it's the right CPT
    if ( 'cpt-slug' != get_post_type() ) {
        return false;
    }
    // Globalize the post object
    global $post;
    // Parent CPT
    if ( 0 == $post->post_parent ) {
        return 'cpt-parent';
    }
    // Not a parent CPT, so fetch current post parent
    $parent = get_post( $post->post_parent );
    // Child CPT
    if ( 0 == $parent->post_parent ) {
        return 'cpt-child';
    } else {
        return 'cpt-grandchild';
    }
}

Parent CPT

The “parent” CPT can simply use the normal loop to display the debate title, content, etc.:

if ( 'cpt-parent' == wpse121567_get_cpt_hierarchy() ) {
    // Normal loop here
    if ( have_posts() ) : while ( have_posts() ) : the_post();
        // Normal loop markup
    endwhile; endif;
}

Child CPT

The “child” CPT can fetch the parent CPT’s comments using get_comments() and display them:

if ( 'cpt-child' == wpse121567_get_cpt_hierarchy() ) {
    // Globalize post object
    global $post;

    // Output Parent CPT title and content
    $parent = get_post( $post->post_parent );
    echo '<h1>' . $parent->post_title . '</h1>';
    echo '<div>' . apply_filters( 'the_content', $parent->post_content ) . '</div>';

    // Fetch parent CPT comments
    $parent_cpt_comments = get_comments( array(
        'post_id' => $post->post_parent,
        'status' => 'approve'
    ) );
    // Loop through parent CPT comments
    foreach ( $parent_cpt_comments as $comment ) {
        // Output comment list markup here
    }
}

Grandchild CPT

The “grandchild” CPT can fetch the Parent CPT’s statistics (using whatever method you choose):

if ( 'cpt-grandchild' == wpse121567_get_cpt_hierarchy() ) {
    // Comment Stats code goes here
}

All in one template file single-{cpt}.php

Putting it all together:

get_header();

// Parent CPT
if ( 'cpt-parent' == wpse121567_get_cpt_hierarchy() ) {
    // Normal loop here
    if ( have_posts() ) : while ( have_posts() ) : the_post();
        // Normal loop markup
    endwhile; endif;
} 
// Child CPT
else if ( 'cpt-child' == wpse121567_get_cpt_hierarchy() ) {
    // Globalize post object
    global $post;

    // Output Parent CPT title and content
    $parent = get_post( $post->post_parent );
    echo '<h1>' . $parent->post_title . '</h1>';
    echo '<div>' . apply_filters( 'the_content', $parent->post_content ) . '</div>';

    // Fetch parent CPT comments
    $parent_cpt_comments = get_comments( array(
        'post_id' => $post->post_parent,
        'status' => 'approve'
    ) );
    // Loop through parent CPT comments
    foreach ( $parent_cpt_comments as $comment ) {
        // Output comment list markup here
    }
}
// Grandchild CPT
else if ( 'cpt-grandchild' == wpse121567_get_cpt_hierarchy() ) {
    // Comment Stats code goes here
}

get_footer();