They were found guilty of conspiring to defraud the United States and deliver misbranded drugs, court records state. The charge carries a sentence of as much as five years in prison. The sentencing is set to take place on 6 October.
While the Grenons represented themselves during their trial, which lasted two days, they chose not to speak, according to the Miami Herald.
Joseph Grenon said the family would be appealing the guilty verdict.
Prosecutors referred to the Grenon family as “con men” and “snake-oil salesmen,” adding that their Genesis II Church of Health and Healing sold $1m of what they called their Miracle Mineral Solution.
They said in videos that the solution would cure 95 per cent of known diseases, such as Covid-19, Alzheimer’s, autism, brain cancer, HIV/AIDS, and multiple sclerosis, according to prosecutors.
But what they were selling was chlorine dioxide, which becomes bleach when it’s ingested. It’s usually used for treating textiles, industrial water, pulp, and paper, the Food and Drug Administration states.
A federal judge in Miami ordered them to stop selling the substance in 2020, but the so-called church ignored the measure.
Jonathan and Jordan Grenon were detained in Bradenton south of Tampa Bay, while Mark and Joseph Grenon were arrested and extradited to the US after fleeing to Colombia.
Jonathan and Jordan Grenon have also been convicted of violating federal court orders instructing them to stop selling the “solution” in 2020. The charges carry a maximum sentence of life in prison, the Miami Herald noted.
But US authorities agreed to drop those same contempt charges against Mark and Joseph Grenon when they were extradited from Colombia.
“This whole Miracle Mineral Solution scheme was built on deception and dishonesty,” prosecutor John Shipley said during closing arguments, according to the Herald.
He added that they “created a fake church to make it harder for the Food and Drug Administration and government to stop them from selling snake oil”.
“This was no church,” he said. “This was a scam for money, an old-fashioned scam.”
“You cannot go out and create a fake church and violate the law,” Mr Shipley said.
In one of his videos, Mr Grenon said, “we are trying to create a world without disease” and that the solution has “been proven to be tremendously effective in curing cancer”.