What does my Thai wife need to apply for a visitor visa to Australia to stay with my mother?

Hello everybody 👋

My Thai wife and I plan to visit and stay with my mother in Australia for a week.

Has anyone done this before?

I understand my wife needs a letter from my mother to say she can stay with her to get a visa.

Is a mother in law considered family to do this?

I don’t know whether my mother has to prove other things like her finances if my wife stays at my mother’s house.

I know my wife has to go to Bangkok to the Australian Emabassy and make an appointment.

It’s a bit complicated trying to follow the process on the Australian government website.

Any help would be appreciated.

Myself I have a New Zealand passport so I don’t need a visa.

Thanks in advance 🙏