A businessman had been gagged and forced to sign over his company before being murdered, the Old Bailey heard.
The defendants are accused of dumping the bodies at sea
Amarjit Chohan, of Hounslow, west London, had also been drugged before being killed and dumped in the sea, Richard Horwell, prosecuting, said.
Mr Chohan and his family were allegedly murdered for his successful business.
Kenneth Regan, 54, of Wilton, Wilts, William Horncy, 51, of Bournemouth, Dorset, and Peter Rees, 38, of Portsmouth, Hants, all deny murder.
Amarjit and Nancy Chohan, their two sons and Mrs Chohan's mother Charanjit Kaur vanished in February 2003.
The jury heard that Mr Chohan's body was found in the sea near Bournemouth pier two months later.
Mr Horwell told the court: "it was obvious he had been restrained. He had been gagged with packing tape."
Tests on the body also revealed "an unusually high level of gammahydroxubutrate - a drug more commonly known as GHB which can be used as a sedative".
Mr Regan is accused of murdering Mr Chohan and his family in order to seize control of his fruit import and export business.
The prosecution alleges Mr Chohan was probably held captive at Mr Regan's home after he arranged a meeting at Stonehenge in Wiltshire last February.
Mr Horwell said that while Mr Chohan was being held he was forced to sign a number of documents and blank sheets of paper.
"He was also forced to record a number of voice messages in an attempt by his captors to placate and reassure his wife and friends."
Documents signed by Mr Chohan, relating to his CIBA Freight company, were then used to convince staff that he had handed over the business, the prosecution claimed.
Concerned by Mr Chohan's disappearance, his wife Nancy repeatedly called his mobile number but received no reply, the court heard.
Mr Regan then allegedly went to the family home and played aloud a message he claimed Mr Chohan had left on his phone saying "Tell Nancy I'm OK and I'll be home tomorrow".
The prosecution claim Mrs Chohan, her two sons, Devinder, 18 months, and Ravinder, two months and Mrs Chohan's mother were then imprisoned then or "as seems more likely, murdered".
Mr Horwell alleged that Mr Regan arrived at the CIBA premises on 17 February with a hand-written letter from Mr Chohan and a Power of Attorney for the running of the company.
The letter, which has since disappeared, said something along the lines of "greed has got the better of me".
"I've got myself in serious trouble. Some people are after me and I have to escape. I fear for the safety of my family."
Nancy Chohan's body was found in the same area as her husband's in July while the body of Mrs Kaur was found in November in a bay off the Isle of Wight.
The bodies of the boys have not been recovered.
The trial continues.