Get grand child pages, sub child pages along with siblings of parents of the current page using page depth calculation

get_child_parent__siblings_page.php

<?php
global $post;
function get_all_subpages($page, $args = '', $output = OBJECT) {
    // Validate 'page' parameter
    if (! is_numeric($page))
        $page = 0;

    // Set up args
    $default_args = array(
        'post_type' => 'page',
    );
    if (empty($args))
        $args = array();
    elseif (! is_array($args))
        if (is_string($args))
            parse_str($args, $args);
        else
            $args = array();
    $args = array_merge($default_args, $args);
    $args['post_parent'] = $page;

    // Validate 'output' parameter
    $valid_output = array(OBJECT, ARRAY_A, ARRAY_N);
    if (! in_array($output, $valid_output))
        $output = OBJECT;

    // Get children
    $subpages = array();
    $children = get_children($args, $output);
    foreach ($children as $child) {
        $subpages[] = $child;

        if (OBJECT === $output)
            $page = $child->ID;
        elseif (ARRAY_A === $output)
            $page = $child['ID'];
        else
            $page = $child[0];

        // Get subpages by recursion
        $subpages = array_merge($subpages, get_all_subpages($page, $args, $output));
    }

    return $subpages;
}
 //print_r($all_current_subpages);
 //$all_current_subpages = get_all_subpages(70);
$args = array(
    'order'          => 'ASC',
    'orderby'        => 'menu_order',
);

$currentpage = $post->ID;
$parentpage = $post->post_parent;
$grandparent = get_post_ancestors($currentpage);
$grandparentID = $grandparent[1];
//echo $currentpage;
//echo $parentpage;
//echo $grandparentID;

$grand_child = get_all_subpages($grandparentID, $args);
$sub_child = get_all_subpages($parentpage, $args);


function get_current_page_depth(){
    global $wp_query;
     
    $object = $wp_query->get_queried_object();
    $parent_id  = $object->post_parent;
    $depth = 0;
    while($parent_id > 0){
        $page = get_page($parent_id);
        $parent_id = $page->post_parent;
        $depth++;
    }
  
    return $depth;
}
//echo get_current_page_depth();

echo "<ul>";
	if(get_current_page_depth() == 2) {
		foreach ($sub_child as $value) {
			//echo $value->post_title ."<br>";
			if($post->ID != $value->ID){
				$sss = get_permalink($value->ID);
				echo "<li><a href='$sss' class='readMoreBtn style_2'>$value->post_title</a></li>";
			}
		}
	}
	if(get_current_page_depth() == 3) {
		foreach ($grand_child as $value) {
			//echo $value->post_title ."<br>";
			if($post->ID != $value->ID){
				$sss = get_permalink($value->ID);
				echo "<li><a href='$sss' class='readMoreBtn style_2'>$value->post_title</a></li>";
			}
		}
	}
echo "</ul>";

?>