@bridgemans
In QBO, 1 company file need a QBO account
https://quickbooks.grsm.io/Australia
If you are more familiar with the unsupported QB Desktop AU version, you may consider using QB Desktop US version with a one time license to create and manage unlimited company files. For Pro 1 user, you may purchase it for US$300 directly, or around US$200 thru a partner/reseller.