phranque - 2:09 am on Nov 20, 2012 (gmt 0)

you can't really "submit a site to google" but you can use the "add a site" button in GWT to add a subdomain to your GWT account.

the sitemap.xml file for each subdomain go in the document root directory of the virtual host for that subdomain.
in your case, these would go in the appropriate subdirectories of public_html.