State Common Paymaster E1 8.12 upgrading to 9.0

After reviewing the online documentation for the State Common Paymaster in the Corporate Tax ID setup, I would like to ask if there is any sample documentation for state common paymaster setup and ask the questions below?

The customer has both scenarios:

Companies share the same tax id for each allowable tax type

Companies with different tax id's use a paymaster group code in UDC 06/PM.

When is a separate paymaster group code required (given the scenario above)?

Is the parent company required in the setup for either scenario? 

Thanks so much.