Hello,
If you add subdomains same as that was added on main domain, then it will create a separate vhost entry for both subdomains under main httpd.conf file but the document root for both subdomains i.e sub1.maindomain.com and sub1.parkeddomain.com would be same i.e. /home/username/publuc_html/sub1.
Both subdomain would show the same contents
Nick J.