score:3
Your friend will likely be applying for the Subclass 400 Temporary Work (Short Stay) visa:
https://immi.homeaffairs.gov.au/visas/getting-a-visa/visa-listing/temporary-work-400
As far as I can tell, there is no restriction that limits them to a single employer, so I would submit the application with both Letters of Invitation attached and request a period of stay covering both jobs. If granted, they are free to travel Australia for tourism etc between jobs:
Combining a holiday with your intended work or activity may be allowed if the holiday is of short term duration and secondary to the main purpose of your visit.