Based on my test, we can use different server names to connect to the same Oracle database using different usernames. So In your scenario, you can use four kinds of server names to meet your requirement. Here I make a test using IP address, servername and FQDN.
Community Support Team _ Frank If this post helps, then please consider Accept it as the solution to help the others find it more quickly.
OF COURSE that Has sense, if were work with ORACLE, you will realise that you have ONE DATABASE and differents schemas ... When you have a RIGTH DATABSE SECURITY ENVIRONMENT, you must have to create different username and password for different schemas, but, POWERBI doesn't have the habilities to create different connection to same Database with different users. I request to Database Team Admin if they can create a "Unified" user and they said, NO... it is a very very weak point in PowerBI if it want run the BI race.