Don't edit the PHP code! This is a setup issue for sure. I just don't know enough about the details to provide an answer yet.
A "parked" domain is one that shares the same web space (file system directory location) as another domain. It has nothing to do with the name of the server box.
Instead, try to edit the includes/constants.php for each site. Locate this:
// If 4images has problems to find out the right URL, define it here.
// define('SCRIPT_URL', 'http://www.yourdomain.com/4images'); //no trailing slash
Uncomment it and set the URL to the root of 4images (where the index.php is located) Example:
// If 4images has problems to find out the right URL, define it here.
define('SCRIPT_URL', 'http://www.example.com/4images'); //no trailing slash
Also try to think about any other details regarding your web site set up. Please provide more details if you can. How about a URL to each web site? No login information, just URLs.