Get child pages of the current page, similarly get details of siblings of a child page along with the details of their parent page in a child page.

get_child_parent_page.php

<?php
global $post;
$args = array(
    'post_type'      => 'page', //write slug of post type
    'posts_per_page' => -1,
    'post_parent'    => $post->ID, //place here id of your parent page
    'order'          => 'ASC',
    'orderby'        => 'menu_order',
);
 
 
$the_query = new WP_Query( $args );
 
if ( $the_query->have_posts() ) {
	echo "<div class='animal_health_welfare_topics'><div class='elementor-row'>";
	while ( $the_query->have_posts() ) {
	$the_query->the_post();
	$getTitle= get_the_title();
	$postURL= get_permalink();
	$src = wp_get_attachment_image_src( get_post_thumbnail_id($post_id), 'large' );
	$url  = $src[0];
	$excerpt = get_the_excerpt();
	$excerpt = substr($excerpt, 0, 150);
	$excerpt = substr($excerpt, 0, strrpos($excerpt, ' '));
	echo "<div class='topic elementor-column elementor-col-50 '>";
		echo "<div class='img_box'><a href='$postURL'><img src='$url'></a></div>";
		echo "<div class='topic_data'><a href='$postURL' class='title'><h3>$getTitle</h3></a><p>$excerpt ...</p><a href='$postURL' class='readMoreBtn style_2'>Read More</a></div>";
	echo "</div>";
	}
	echo "</div></div>";
}

else {
	if ( $post->post_parent ) {
		echo "<div class='animal_health_welfare_topics'><div class='elementor-row'>";
		$parentpost = get_post($post->post_parent); 
		$parentImgsrc = wp_get_attachment_image_src( get_post_thumbnail_id($post->post_parent), 'medium' );
		$parenttitle = $parentpost->post_title; 
		$parentImgurl  = $parentImgsrc[0];
		$parentpostURL = get_permalink($parentpost);
		$parentexcerpt = $parentpost->post_excerpt;
		$parentexcerpt = substr($parentexcerpt, 0, 150);
		$parentexcerpt = substr($parentexcerpt, 0, strrpos($parentexcerpt, ' '));
		echo "<div class='topic elementor-column elementor-col-50 '>";
		echo "<div class='img_box'><a href='$parentpostURL'><img src='$parentImgurl'></a></div>";
		echo "<div class='topic_data'><a href='$parentpostURL' class='title'><h3>$parenttitle</h3></a><p>$parentexcerpt ...</p><a href='$parentpostURL' class='readMoreBtn style_2'>Read More</a></div>";
		echo "</div>";
		
		$siblings = new WP_Query( array(
            'post_type' => 'page',
            'post_parent' => $post->post_parent,
            'post__not_in' => array( $post->ID ),
			'order'          => 'ASC',
			'orderby'        => 'menu_order',
			'post_parent__in' => array( $post->post_parent ),
        ) );
        if ( $siblings->have_posts() ) {
			
			while ( $siblings->have_posts() ) {
				$siblings->the_post();
				$getTitle= get_the_title();
				$postURL= get_permalink();
				$src = wp_get_attachment_image_src( get_post_thumbnail_id($post_id), 'medium' );
				$url  = $src[0];
				$excerpt = get_the_excerpt();
				$excerpt = substr($excerpt, 0, 150);
				$excerpt = substr($excerpt, 0, strrpos($excerpt, ' '));
				echo "<div class='topic elementor-column elementor-col-50 '>";
				echo "<div class='img_box'><a href='$postURL'><img src='$url'></a></div>";
				echo "<div class='topic_data'><a href='$postURL' class='title'><h3>$getTitle</h3></a><p>$excerpt ...</p><a href='$postURL' class='readMoreBtn style_2'>Read More</a></div>";
				echo "</div>";
			}
		}
		echo "</div></div>";
	}
}
wp_reset_postdata();?>