I am a descendant of James Young who was buried at the old cemetery. He owned the place when it was called Hamilton having bought it from Sarah Maria Hamilton in 1850. John Cockburn Johnstone was his son-in-law. I don't know who George Smith or William Brown were but family stories say they were men who worked on the property which at that stage was a vineyard. The last burials of the total of six graves were Dr Carlyle who died on 8 Sept 1844 and Claudia, the young daughter of Mrs Hamilton. There is a memorial to Dr Carlyle inside St Thomas Church in Port Macquarie. I don't think any of them were convicts. The graves were originally where the caravan park is now - the headstones were moved some years ago and now there are only four of them. Hope this fills in gap or two for you.
Regards, Jennifer Willmott.