Unlike an SMS, receiving a call to an Australian mobile number when overseas is not free, unless via Wi-Fi calling, which is currently available when roaming only to those using Telstra's network here (e.g. Boost)
Using your secondary sim for Wi-Fi calling with your primary is only possible if the secondary is not roaming, so likely local to its location
If you have a VoIP provider like Crazytel for your fixed/landline phone number, then you could divert your Australian mobile number to it, and receive (as well as make) calls via their app, which also allows you to set its caller ID as your mobile number
www.crazytel.com.au