I'm involved with an Australian Pty Ltd company that is the applicant for an Australian patent, and has listed the two inventors as two of the shareholders of the company. Does the Pty Ltd have co-ownership rights to the patent, or do those rights need to be granted by a license?
You are mixing a few things up there.
Inventor != applicant:
Inventor is the person that invented the invention, applicant is the person that applies for the patent and therefore is the owner of the patent (e.g. the employer). The compensation for the inventor has to be agreed upon between those two.
In your case that would (probably) mean that the company owns the patent. You should however make sure (ask) that is the case as sometimes changes in the ownership don't get mentioned to the patent office or there could be other constructs where the company is the applicant but essentially owns only a part of the patent, or any revenue generated goes to the inventors, or whatever.
A license allows somebody to use - in the terms of the license - (e.g. produce and sell or produce for himself) the invention without getting sued for that, but it does not grant ownership of the patent nor does it entitle to any more right.
If the company does not own the patent, the inventors beeing shareholders could retractively protect the company from getting sued if they can prove there was an implicit license where the shareholders knew and where okay with the invention beeing produced, but thats a rather dangerous way, so an explicit license should be negotiated then.