Hi Banno, this is a really good question!
Each QuickBooks online file is designed for one company only, single ABN. We, however have the option to produce invoices with different logos and details on the template.
This can be achieved by customizing the templates you want to use in a .docx format and then import this template to QuickBooks. Please refer to the link below for the detailed instructions on achieving this. Hope this helps.
https://quickbooks.intuit.com/community/Getting-started/Import-custom-form-styles-for-invoices-or-es...