When referencing PEO website material:

Author: Parliamentary Education Office (PEO)
Date of Publication: 2019
Title: use the name of the resource, followed by the type of resource or the series name. For example, The Constitution (video) or Parliament and Congress Closer Look.

An example using the Harvard referencing style;

Parliamentary Education Office (PEO) 2019, Amendments Fact Sheet, viewed 20 January 2019, http://www.peo.gov.au/learning/fact-sheets/amendments.html