For phpMyAdmin, I believe you would have to setup separate copies (in each domain) and edit the config.inc.php (I think that's the name), there are 3 config items to change:
Code:
$cfg['Servers'][$i]['user'] = 'username'; // MySQL user
$cfg['Servers'][$i]['password'] = 'userpassword'; // MySQL password (only needed
// with 'config' auth_type)
$cfg['Servers'][$i]['only_db'] = 'somedatabasename'; // If set to a db-name, only
// this db is displayed in left frame
// It may also be an array of db-names, where sorting order is relevant.
The 'username' can actually be whatever user was created when the package was installed (such as osCommerce, osTicket) to administrate that particular database. Otherwise you will have to create the user/pass in the mySQL database and make the appropriate changes to it's tables and priv's etc (much more messy).
Since they will be in separate domain folders, when a particular domain user browses to that URL:
https://www.example.com/phpMyAdmin
(hopefully password protected directory...! Adds login prompt, and is much safer IMO)
They have to authenticate the protected dir prompt, then phpMyAdmin will open up and only show them the singe database you specified (or the array of databases), it will have connected to mySQL using the ftpusername and password you configured in that particular directory.
Access to (remote DB) -I assume you mean not on the same server. As long as the remote server has mySQL setup for remote access and port 3306 is open in the firewall, you should be able to connect to the mySQL on the remote server. For more information, please search the forums (mysql, 3306, remote, etc)