I just came across this post and I soon remembered seeing a book my father had on Colonel John Okey. I believe he still has it. My elder brother is named John, too!
I also remember seeing a replica tombstone of William Okey at Old Sydney Town. He was a convict sent to Australia for stealing. If I remember correctly, the local Aborigines speared him to death after he stole one of their canoes whilst trying to escape!
I also remember that my Grandfather did quite an exhaustive family tree back to Colonel John Okey.
I will chase these details up and post a clearer reply as soon as I can.