echo custom post terms (grandchildren only)

I have a taxonomy with hierarchical terms (parent, children, grandchildren).

Now I want to show each custom posts taxonomies terms (in single.php and archive.php), BUT only grandchildren and as comma separated links.

I already tried get_the_terms_list and wp_get_post_terms, but it seems they both lack $args to pull it off. Something like “childless” from get_terms.

Is it even possible to echo a posts taxonomy terms, but only grandchildren?

Thanks