If you're only seeing the username in the grid that is the same user as the logged in user this has to do with the security for the userrole that is assigned to the user. By default the user will only have permissions to see and manage their own account. So when you create a userrole standardUser (e.g.) and assign this to a user and show the user a grid of users the user will only see the data for his own record. This is because under the security settings for the role the user management section will have selected roles ticked and none of the roles selected. For the standardUser role you'll need to indicated which of the users he can manage and then you'll see the usernames coming up.
If you do not want the user to manage other users then you can use the fullname from the Administration.Account entity, this name does not have the above mentioned restriction.
For more information on user roles see link
I'm a little unsure of what you are asking. Are you attempting to search by Order Name and return a list of Orders matching that search criteria, along with who ordered it (the Customer)? If so, your data grid would be source Database-Orders, and you'd have a column for the association to the Customer.