How can I let 2+ domains point to the same document root?

If you want to point more than one domain to a document root, you need to edit the domain_aliasses table in the DB.

Open your PMA and set alias_mount to / and the status from ok to change on the according domains.

After that change run the ispcp-rqst-mngr under /var/www/ispcp/engine/

WARNING

If you're later going to delete one of those domains, the directory will be deleted, too.