Chambers had invested in California-based entrepreneur Jim Bilbrey, who claimed to have invented a water-powered engine.
When Bilbrey's business failed and the Chambers family investment was lost, they were contacted by a New Jersey-based businessman Alex Schleider, who claimed to have lost $500,000.
Schleider told the Chambers they would stand a better chance of getting their money back if they joined forces.
He befriended their son Julian Chambers, who was studying for a Master's degree in the US, and was soon offering fresh investment opportunities.
In early 2012, amid the hype of Facebook initial public offering (IPO), Schleider claimed he had access to shares at a discounted price before they went on sale to an initial public offering, or IPO.
The offer was particularly attractive because large blocks of Facebook shares were extremely difficult to get, and they were expected to increase in value quickly.
In emails to the Chambers, Schleider referred to his business partner "Eli". "Eli" was in fact Eliyahu Weinstein, who was on bail for duping members of his own synagogue, Brooklyn's Kahal Minchas Chinuch, in a $250m Ponzi scheme.
Gerald Chambers told the Herald on Sunday they had no idea Weinstein was behind the scam until much later.
"We were dealing with [Schleider] and it just so happened that he was associated with a big-time fraudster [Weinstein] that we didn't know, didn't know his name."
Court papers show on February 1, 2012, Schleider emailed the Chambers to say: "Eli has an interesting deal involving Facebook's IPO let me know if you guys have an appetite?"
The Chambers took the bait, wiring $1.5m to buy 40,000 Facebook shares at $37 a share a few days later, the court papers show.
The smooth-talking Jersey boys claimed the deal was watertight - they bought the shares through an investment company and it was guaranteed by a $15m investment in Park Lane apartments.
Nine days later, Schleider emailed Gerald and Julian to say he and "Eli" were buying more shares, this time at $40 a pop.
"Hopefully the stock goes to US$150! And you recoup all of the Bilbrey losses!!"
Schleider stressed the deal was closing and time was of the essence, and the Chambers invested a further $2.06m.
Then in early March, Schleider wrote that another tranche of Facebook shares was closing.
Again emphasising urgency, Schleider emailed that "word on the street" was a US financial watchdog was about to clamp down on this lucrative "secondary market" in Facebook shares.
"BTW they are toying with the idea of selling the stock we purchased at $30 when it hits $50."
The carrot dangled, the Chambers threw in a further $2.26m.
Between February 6, 2012 and March 4, 2012, Chambers invested $5.8m, which the family would later find out would be laundered in sham companies and used to fund Eli's legal troubles, according to the court documents.
However, the fraudsters weren't done yet.
Schleider then persuaded the Chambers to invest more than $3m in a Florida apartment complex. They returned about $2m to the Chambers, claiming it was a return on their Facebook shares.
Chambers, realising his investment was vanishing, flew to the US in February to confront him.
His son Julian secretly recorded the meeting at the Marriott Glenpointe Hotel in Teaneck, New Jersey.
In the transcript Weinstein is heard telling them "you've got to trust me".
"It's going to be hard for you because I'm the bad guy. I'm the thief. I only made Schleider money and I made you money."
"Where is it?" demanded Chambers.
"You made it!" insisted Weinstein. "I wired it back to you. I didn't wire you money?"
Gerald Chambers told the Herald on Sunday the secret recording proved a crucial part of the FBI's case. "That's what canned him," he said.
In January last year, Weinstein pleaded guilty to wire fraud conspiracy and money laundering in connection with the unrelated Ponzi scheme.
Unfortunately, most of the Chambers' millions had already been laundered through a network of "co-conspirators".
Weinstein had used it to pay his mounting legal fees, take his home out of foreclosure, and send his children to religious school - as well as fund his own investments, including a gold deal in Africa, the court papers say.
Weinstein emerged as the ringleader of the Facebook scam.
According to the FBI, he spent a decade creating and executing a series of elaborate fraudulent investment schemes, taking advantage of his closest friends in New Jersey's ultra-orthodox Jewish community.
The "real estate developer" would convince friends to invest in properties he claimed to own, and then refuse to pay them back or offer only a fraction of what was owed.
"This community is tight-knit; its members are connected to each other from a young age through numerous types of social and religious bonds," said Karl Ubellacker, an FBI special agent, in documents filed with the New York Supreme Court.
"Weinstein has exploited the social and business customs and practices of this community in furtherance of his scheme."
According to court documents, when confronted by one victim at his home, Weinstein asked the man what he [Weinstein] had in common with the man's wife.
When the person said he didn't know, Weinstein replied: "We both f***ed you."
Weinstein used the victims' money to amass a $6.2m watch collection, art, and $14m worth of jewellery and Judaica, or Jewish historical materials. He kept multiple passports and boasted that he could disappear at any time.
Most of the wealth has been stashed in the US and Israel.
Schleider, 48, of New Jersey, and Aaron Glucksman, 41, of Brooklyn, New York, have pleaded guilty to charges related to their roles in the scheme.
Glucksman was sentenced to 52 months in prison. Schleider is awaiting sentencing.
US Attorney Paul J.Fishman said: "Even while facing federal charges that eventually netted him decades in prison, Weinstein couldn't resist the buzz around the Facebook IPO and the opportunity to fleece unsuspecting investors.
"Shamelessly, he even used the money he stole to pay the legal fees he accumulated from the previous scam."
Already facing a 22-year sentence for the $250m Ponzi scheme, Weinstein pleaded guilty in a New Jersey district court this month to defrauding the Chambers.
He is due to be sentenced on these charges in December.
After the charges, FBI Special Agent Aaron T. Ford offered a few pearls of wisdom, warning in a press release if "an opportunity seems to be too good to be true, it probably is".
Last year, the Chambers launched a civil litigation in the New York Supreme Court against 27 defendants including the fraudsters, rabbis, law firms and the congregation of an Orthodox Jewish synagogue in New York.
Chambers' lawyers allege the rabbis and synagogue defendants benefited from Weinstein's fraud and were well aware the deals were "not kosher".
But with the principal targets in prison or awaiting sentence, attempts to recover their money will be tricky.
They have had attempts to sue Weinstein's law firm struck out, and have appealed.
Chambers' US attorney Daniel Richland invoked biblical references to describe the betrayal. "This foundation of trust and friendship, built over the course of a year, was a facade; a veneer hiding Schleider's true purpose: to extract from [the Chambers] their financial resources in fake investments," he claimed.
"Like the serpent in the Garden of Eden, it would be defendant Schleider who would lead them to ruin and perdition and the loss of [millions] through his lies, blandishments, and fraud."
Richland described his clients as "not sophisticated investors" from the backblocks of rural New Zealand.
"Gerald Chambers is a sheep farmer residing in New Zealand [whose] investment experience in the US is limited."
The Chambers are far from your average farming couple. Their residence is called "Chequers" - the same name as the British Prime Minister's country estate - and the family own an investment company, Saskatoon Financial, in the Cayman Islands.
In 1976, Chambers was kidnapped by men "working in Jamaica's interest" after he allegedly took $3.1m - more than $10m in today's money - out of the country when he worked for a Jamaican firm in liquidation. Chambers had done nothing wrong and says he was the victim of a political-motivated kidnapping.
"I've never done anything wrong, I was kidnapped, the guys got charged, they got seven years."
In 2001, Reuters reported he was the victim in an attempted $4.6m fraud by a priest from the Greek Orthodox Church in Cyprus.
The case collapsed when Chambers refused to testify against the priest, known only as Chrysanthos.
In spite of it all, the Chambers' daughter, Kimberley Chambers, New Zealand's top female long-distance swimmer, still has a Facebook account.
