Under QLD law, tenants have 7 days to catch up on rent before you can give them a notice to remedy breach. If they comply, all well and good. If they don't you can then start eviction proceedings (Form 11 I think).

Unfortunately it sounds like the tenants aren't the only slack ones – it might be a idea to start shopping for another property manager.

Also, as far as I'm aware eviction disputes are usually taken up with the RTA, not the courts?

Interesting side note – squatting laws in QLD/Australia mean that even if the tenants are evicted, they may still be able to stay in the property – provided that one of them remains there at all times, otherwise as soon as it's vacant the police can move in and repossess the house.