Qantas notes on its website and also Pointhacks article on Oneworld that in order to be eligible for oneworld, you need at least two oneworld airlines in your itinerary.
This emphasis is “at least”. Does this mean I can also combine non-oneworld airlines too?
If you are referring to the OneWorld Award, then no.
As per the Qantas website
The one world Classic Flight Reward table only applies when your Reward Itinerary includes travel on at least two one world Member Airlines other than Qantas, and does not include any travel on any airline that is not a one world Member Airline.