I think this is what’s happening. You’re being charged 179,000 points for the flight from Melbourne to Gothenburg, and 177,400 points for the return flight from Gothenburg to London. For each flight, something very similar is happening – namely, Qantas is charging you points for the final flight of each leg separately. To elaborate:
For the flights to Europe, you’re using KLM for the final leg. KLM and Qantas have a bilateral partnership, but KLM isn’t a Oneworld airline. Because the flights to Amsterdam via Hong Kong constitute a “Oneworld” award using Qantas points, and the flight from Amsterdam to Gothenburg does not, Qantas is charging you 159,000 points for the flights to Amsterdam, and an extra/separate 20,000 points for the KLM flight to Gothenburg. Total: 179,000 points.
For the flights from Europe, something slightly different is happening. You’ll notice from looking at Qantas Classic Flight Reward tables that Qantas Classic Flight rewards and British Airways Classic Flight rewards are on different tables. As a result, the Qantas Flight and the BA flights can’t be combined on the same reward. So Qantas is charging you 159,000 points for the BA flights from Gothenburg to Sydney via London, and then an extra 18,400 points for the Qantas flight to Melbourne.
This is finicky and complicated – I can understand your confusion! The bottom line: to save yourself 38,400 points per person, I’d use points to fly from Melbourne to Amsterdam and Gothenburg to Sydney on Cathay Pacific and British Airways respectively, then I’d either pay money for the short domestic flights, or use points to book economy reward flights. Business class probably isn’t worth it for such short flights.
Hope this helps!