Schapelle's half-brother, James Kisina, who accompanied her on the trip to Bali, was jailed for four years in 2006 for his part in a burglary in Brisbane during which money and drugs were stolen and a couple were attacked with an iron bar.
Two old friends of Michael Corby told Duff he began growing and selling marijuana in his mid-20s.
Duff said yesterday it was not clear whether Schapelle knew the drugs were in her bag. However, he added: "I think it's fair to say that she was well aware that her father was entrenched in the marijuana game for three decades."
Duff believes Schapelle's affection for her father - who always denied knowledge of the drugs - prevented her from revealing the true story.
"This is a very, very close family and they're a very close father-daughter relationship," he said.
McCauley, who served 15 months in jail for running drugs, visited Schapelle in prison soon after she was arrested.
The purser on Schapelle's Qantas flight, Gail Burgess, told Duff she was "aggressive and loud". The crew stopped serving her drinks after passengers complained. Alexander Downer, Minister for Foreign Affairs at the time of her arrest, says Australian Federal Police told him they believed Schapelle was guilty.