is there anything in Joomla that decides how the names will be displayed?
No sorry, Joomla have a unique field called "name".
With Easy Profile you can split name in firstname,secondname and lastaname. Easy Profile simply concatenate these parts and store in Joomla "name". You can customize the views (with Joomla template override feature) of Easy Profile to get "Last, Firstname", but this will work only on profile page (frontend) and users list (frontend).
Alternative is to write a plugin (based on our skeleton plugin) to store name in your format after update/registration profile:
- Download, install and enable our skeleton plugin, you can download from
https://www.easy-profile.com/docs/44-triggers.html
- open file /plugins/jsn/skeleton/skeleton.php
- remove examples functions: triggerFieldAvatarUpdate, triggerProfileUpdate
- Write your function like this
triggerProfileUpdate($user,&$data,$changed,$isNew){
$name=$data['lastname'].", ".$data['firstname'];
$db=JFactory::getDbo();
$query="UPDATE #__users SET name='".$db->quote($name)."' WHERE id=". (int) $user->id;
$db->setQuery($query);
$db->execute();
}
NOTE: this code is not tested and not supported, this is only for example purpose. to write a plugin you need PHP and Joomla dev Knowledge