(a) That's right. The two self-governing territories have been given their powers of self-government by means of laws enacted by the Commonwealth (federal) government.
The other terrritories are governed directly by the Commonwealth government.
Note: Norfolk Island enjoyed limited rights of self-government between 1979 and 2015. However, the Norfolk Island Legislation Amendment Act 2015 (Cth) put an end to self-government and placed Norfolk Island under similar governance arrangements as Australia's other offshore territories.