Hello,
What are mean by templates are non xml files?
If you want template B get back the date from template A then we have to give the option to user enter file name to get the template A from SharePoint. We have to write the code to load the template A using SharePoint URL with file name.
Otherwise while creating the template B from we have to store template A file name in one field template B form. Whenever user clicks button then we have to load the template A details in template B form.