Who are the Biloela Family and why are they in the centre of Australian discourse now?

Over some three years, as the government was pressured to address the Murugappan family's plight, subsequent Home Affairs and Immigration ministers have stuck fast to the view that the 'Biloela Family' aren't eligible to resettle in Australia. But who are the Tamilians in the centre of all this?

The Murugappan family consisting of Nades, Priya, Tharnicaa, and Kopika. Source: Home to Bilo/Facebook