Denaro, 54, is considered the most powerful figure in Cosa Nostra, the real-life Sicilian crime syndicate depicted in the Godfather movies.
He has been on the run since 1993 from authorities who want him jailed for a string of crimes including dozens of murders.
Police said Tuesday's arrests followed an investigation which established that the sequestrated companies were ostensibly clean fronts to enable two mafia clans to win public construction contracts via rigged tenders.
Police said Denaro controlled the division of the contracts, which included renovation of a hospital and the building of a wind farm in western Sicily.
The arrests were described by the police as a “tough new blow” to the mafia boss's entourage, but there was no indication they are any closer to catching the elusive mobster who once boasted of having killed so many people he had “filled a cemetery”.
In August 2015 police arrested 11 people said to have been close to Denaro and revealed that the fugitive boss had communicated with them through the age-old method of coded messages written on tiny scraps of paper, or “pizzini”.
Police established that he had been staying at a farmhouse near Mazara del Vallo but were unable to apprehend him.
In 2013, three cousins, a nephew and a sister said to have run Denaro's business activities were arrested but their detentions did not herald a breakthrough in the hunt for the prime target.
Denaro is thought to have succeeded notorious godfather figures Toto Riina, who has been in custody since 1993, and Bernardo Provenzano, who died in prison in July, as the head of Cosa Nostra.
Known for his ruthlessness, he also had a reputation as a womanising playbody with a penchant for flashy cars. The last photographs of him in public circulation date from the early 1990s.
Theresa Principato, a Sicilian prosecutor who spent ten years on Denaro's trail, said in an interview last year she believed he had escaped capture with the help of protection at a very high level.
She also claimed that he travelled regularly on mafia business to countries including Britain, Brazil, Austria and Spain.