@surenk - Have you checked video on this page https://experienceleague.adobe.com/en/docs/experience-manager-learn/sites/seo/sitemaps which defines setting sitemap at different paths? This can be done using AEM's OOTB sitemap generator and as mentioned here https://github.com/apache/sling-org-apache-sling-sitemap?tab=readme-ov-file#content-model you need to set sling:sitemapRoot = true for /cards and /resources pages from page properties.
By using AEM OOTB's sitemap, you adhere to sitemap's schema and it takes care of generating the index files which will be used by search engines.
If you have enabled sling:sitemapRoot = true on
/content/project/us
/content/project/us/cards
/content/project/us/resources
Now when you open index file https://domain.com/content/project/us.sitemap-index.xml it will give you something like this
<sitemap>
https://domain.com/content/project/us.sitemap.xml
</sitemap>
<sitemap>
https://domain.com/content/project/us.sitemap.cards-sitemap.xml
</sitemap>
<sitemap>
https://domain.com/content/project/us.sitemap.resources-sitemap.xml
</sitemap>
If the sitemap urls e.g. https://domain.com/content/project/us.sitemap.cards-sitemap.xml doesn't meet your need, you can see if you can rewrite the urls based on some logic.
If this still doesn't work then you can go for custom sitemap generater based on your own logic in AEM as briefly described here https://www.albinsblog.com/2017/03/how-to-generate-sitemap-for-multi-site-environments-cq5-aem.html