You will define the other two ledgers as a normal (Primary) ledger through Accounting Setups -> Create Ledger screen.
Reporting Ledgers and Secondary Ledgers are two different things.
Common Attributes:
Both Reporting Ledgers and Secondary Ledgers are attached to a Primary Ledger.
Journals are automatically mirrored in both kind of ledgers
Differences:
Reporting Ledgers could only differ in Currency with the Primary Ledger. While, secondary Ledgers could differ in any of the Cs from the Primary Ledger.
Summary:
If you need a representation of your ledger in another currency then you will report a reporting ledger.
If you need another representation of your ledger where other Cs differ as well besides the currency then you will create a secondary ledger.