content-home.php seems to have the code for creating the thumbnails:
$thumb = get_the_post_thumbnail( $post->ID, ‘post-thumbnail’, array( ‘title’ => esc_attr( get_the_title() ) ) );
$thumb = wp_get_attachment_image( $attachment->ID, ‘post-thumbnail’, false, array( ‘title’ => esc_attr( get_the_title() ) ) );
$thumb = ‘<span class=”no-thumbnail”>’ . get_the_title() . ‘</span>’;
somehow combine the code in that last one into the first two thumbnail options.