Yes, but it’s not a good solution, because if the first image is very large, the page loading will be slow down.
If you really want to do that, you need to edit post-grid.php, find the following code
<a href="<?php the_permalink();?>"><?php the_post_thumbnail('fluid_thumbnail',array('alt'=>esc_attr(get_the_title()),'title'=>esc_attr(get_the_title()),'class'=>'scale'));?></a>
Replace it to:
echo van_auto_thumbnail();
However, if you changed the code, you have to make the same changes again if you update the theme to next version in the future.