Sorry it took so long to respond to this question.
The reference to one of your questions, the eastern Sepia species of Australia, is taken from:
Lu, C.C. (1998) Order Sepioidea, pp 504-514 in Besley, P.L.; Ross, G.J.B.; Wells, A. (Eds) Mollusca: The Southern Synthesis. Fauna of Australia. Vol. 5. CSIRO Publishing: Melbourne, Part Axvi 563 pp.
Lu actually refers to the following (for the entire Australian region). I'll let you figure out what you can expect to find in any particular region.
Northern Australian region: Sepia cottoni, S. elliptica, S. latimanus, S. opipara, S. papuensis, S. pharaonis, S. smithi, Metasepia pfefferi, and Sepiella weberi.
Southern Australian region: Sepia apama, S. braggi, S. chirotrema, S. cultrata, S. dannevigi, S. hedleyi, S. novaehollandiae, and S. rex.
Eastern Overlap Zone: Sepia mestus, S. plangon (extends to Gulf of Carpentaria), S. rozella, S. whitleyana (extends to Gulf of Carpentaria), S. baxteri, and S. mira.
And finally, the Western Overlap Zone: Sepia irvingi, S. vercoi, and S. reesi.
Regarding the octopus fauna of Australia .... well, there are so many reports out there of numerous new species that it is difficult to know. We'll just have to wait for a monographic review of the fauna.