@Rēndy0
I would offer an interim cleaning (at a fee). This way, you can check if the guests are keeping the loft clean and address any issues immediately. Maybe once a month isn't frequent enough. When I have long-term guests I try to agree on weekly, 10 days or every 14 days.
I don't know the legal situation in Australia, but I would also inquire whether a longer stay gives the guest tenant rights.