Two crew on medical ops would be great but in many cases can prove a hinderence.
The medical fit out in most of these aircraft substantially increases the operating weight well in excess of any passenger config.
Problems already exist where teams of medics are unable to be transported due to this limitation and prevailing conditions.
A second pilot would only hinder this situation further.
Secondly, money is a big issue. The RFDS is a not for profit organisation and relies on government subsidies and donations in large. Although the efforts of fund raisers is truely commendable, operating a service with king airs and pc12s is not cheap and can demand far more money than can be donated.
Finally, with no offence to the low time pilots out there who are quite capable at there trade. A second pilot in these air craft with a great deal less experience than the PIC would not be of great help in the demanding environment that medical pilots find themselves in on a day to day basis. Look at Monarch for your examples. It could very well have saved the situation in MTG but it could also have compounded it. These aircraft are configured to be flown single pilot and when done right, can be managed very well.