get posts by multiple categories via slug
<?php $args1 = array( 'posts_per_page' => 6, 'offset'=> 0, 'category' => array(2,3,25,30));
$myposts1 = get_posts( $args1 );
foreach ( $myposts1 as $post ) : setup_postdata( $post ); ?>
<div class="each-post col-lg-aynk col-md-aynk col-sm-aynk col-xs-aynk">
<a href="<?php the_permalink(); ?>">
<h2><?php the_title(); ?></h2>
</a>
<a href="<?php the_permalink(); ?>">
<div class="news-story-img">
<?php if (class_exists('MultiPostThumbnails')) : MultiPostThumbnails::the_post_thumbnail(get_post_type(), 'secondary-image'); endif; ?>
<?php the_post_thumbnail( get_permalink() ); ?>
</div>
</a>
</div>
<?php endforeach;
wp_reset_postdata();?>