I have a problem when adding external sitemaps to Yoast. I've managed to successfully add all my external products (which are hosted on a different project) using the wpseo_sitemap_index filter.

add_filter( 'wpseo_sitemap_index', 'add_sitemap_custom_items' );

When i generate a sitemap with yoast, it groups the other posts and taxonomy together. I would like to accomplish this feature with my external sitemaps i have added.

As of right now, it lists the group sitemaps, then it list all my external sitemaps individually, i would like to try to group them together, something like:


And when i click on it, it only shows all my products.

Is this posible? Thanks in advanced

Note: I am on a multisite project, don't know if this has to do anything with it.