2. Are you both still lawfully in Australia?
(that is, are you both fully compliant with all the conditions of your respective visas?)
3. Can you satisfy the authorities that you are what you claim to be?
Have a read of this and this.
And then, take yourselves to see a lawyer
who is also a Registered Migration Agent.
There will be professional fees to pay, in addition to any costs of any applications(s).
Yours is not a factual scenario that is new or unusual.
But it will need to be genuine.