The idea :
Using an extracted data from one sitemap, to use in another one.
For example :
1st sitemap (with ID 1) extracts {Product_ID], {Product_name],
2nd sitemap url :url/[sitemap_ID][Product_ID]"
It will be great because we can make interaction between extracted datas from each sitemaps.
And because these url construction is very common.
And integrate it on an api call will be the must.
Best Regards.