According to the Australia's Department of Home Affairs (excerpted):
ImmiAccount is the front door to our online services. ImmiAccount accepts all online visa and citizenship applications except for Electronic Travel Authority (ETA) applications.
Can I submit multiple applications and/or payments in ImmiAccount?
Yes. ImmiAccount will let you submit multiple online applications and pay for these applications at the same time. For example, if you and your family are applying for visitor visa applications, one member of the family can create and manage all the applications through their ImmiAccount, and pay for all these applications at once. Payment can be made by credit card in Australian Dollars (AUD) for all online applications submitted through ImmiAccount.