@Paul10930.Paul, as a fellow landlord (who does directly manage tenants as well as being an STR host) I'm sorry to hear. Ideas:
As you know STRs in Gold Coast area now often require registration. https://www.houst.com/blog/short-term-regulation-gold-coast
Does the former SH have this and if yes, when did they get it? If not or you can prove they didnt comply with exemptions, you could try making a complaint to the GCC Council (and whatever QLD dept deals with registration complaints). If the host was properly complying then yes, maybe out of luck.
Re subletting I'm really suprised there wasnt at least the wording "with the owners consent" Or was this a more casual tenancy arrangement? I always use the state based standard lease as a starting point. Helps when there have been so many changes to tenancy laws and also the overlap with short term rentals (think privacy, fire safety, bonds, pets etc).
Finally, you have a co host. I assume this is someone you now trust? Just check you are aware of what information/permissions are in your Airbnb settings for your co host to access.