How to create two domains on the application server for the same database...

We are attempting to configure the External Applicant Access in Candidate Gateway. According to the Oracle "How to Setup the External Applicant Access in Candidate Gateway [ID 652694.1]" document we are to "Create two domains on the application server for the same database. On the web server create two instances of PIA connecting to each of them."

Is there documentation on how to do this or can you provide more specific instructions?

Our Dba has responded with the following questions when asked to provide this configuration:

I was referring to MOS doc ID 652694.1 when I was reading about configuration of candidate gateway. I don’t understand step one (create two domains on the app server for the same database). I am not sure why we need to app server instances and 4 PIA instances (two PIA instances to each domain). I am also not certain exactly how to set up two app server domains to the same database. Does the domain name stay the same? Does it change? Does it need its’ own PS_HOME or should it be shared with the original domain?