The supporting documents for tourism/leisure/exploring the US are:
Yes, you can sponsor a friend for a tourist visa.
The transit visa allows people to be in Australia for 72 hours. It is known as Subclass 771.
No, one application is not enough for the entire family. Each person must fill up the application for a temporary resident visa. They must sign this along with other forms. You may submit the applications for all the family members in a single envelope.
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