The "lucrative business" was heavily criticised by the Crown Prosecution service after the men were jailed for more than 10 years at Preston Crown Court on Thursday.
The court heard how ringleader Cristian Vasile, 34 ran the four brothels where at least four Romanian women worked.
Brothers Cristian Stan, 31, and Ionut Stan, 32 managed the ‘day-to-day running’ of the business, taking bookings from punters and acted as bodyguards.
They ran brothels from houses on Mickledon Avenue in Preston as well as on three streets in Blackburn.
Lucy Scully, Senior Crown Prosecutor for the CPS North West Complex Casework Unit said: “These three men ran an extremely lucrative business by exploiting women who they managed as prostitutes. They trafficked the women by transporting them to and from the houses where they worked and also by providing them with homes.
“Christian Vasile was above the Stan brothers in the chain of command. They assisted him by managing the brothels and the phones which brought in customer bookings; they also had relationships with two of the women in order to further exploit them.
“The evidence against the men was overwhelming which meant they had no other choice but to plead guilty. Utility bills and tenancy agreements connected them to the brothels; various phones seized by the police showed that a menu of sexual services had been advertised on various adult websites.
“Ionut Stan was out of the country for a substantial time during the time period, where he received some of the profits which were transferred out of the UK. Photographs show him handling large amounts of Euros and Pounds.
“Following the sentence they must now face up to the consequences of their appalling actions.
"All cases of human trafficking are extremely serious, complex and require sensitive handling. The CPS will continue to work with the police and our international partners to bring to justice those who commit such offences.”
Christian Vasile was sentenced to five years imprisonment for causing or inciting prostitution for gain and two counts of human trafficking.
Christian Stan was sentenced to three years and two months imprisonment for human trafficking.
Inout Stan was sentenced to three years and four months imprisonment for human trafficking.
It began when officers raided the address on Accrington Road, Blackburn, on Wednesday, May 11 2016 as part of an on-going investigation.
Two women in their twenties were found inside and were suspected of being trafficked to the UK from Romania. Safeguarding and welfare issues were addressed, but the women refused to make any complaints against the men, and did not identify themselves as being victims.
Brothers Ionut and Cristian Stan, and the third man Cristian Vasile, were arrested on suspicion of human trafficking for sexual exploitation and later charged.
Officers working under Op Proteus, a dedicated team working to identify both the victims and perpetrators of trafficking and slavery across Lancashire, uncovered that the Stan brothers had trafficked the women from Romania. Once at the address in Blackburn they arranged for the women to be sexually exploited as prostitutes for their own financial gain.
Meanwhile Vasile was found to be the ring leader behind the trafficking and the exploitation, setting up advertising accounts on websites offering services from the women, arranging the wording, photographs and the payments.
DS Tony Atkins from Lancashire’s modern slavery and human trafficking unit, said: “This was both a complex and challenging investigation, but through dedication, tenacity and close working with the CPS we have secured this fantastic result, one of the first we think under the Modern Slavery Act without victims supporting the prosecution.
“These men are dangerous criminals who have no thought or consideration for their victims. These sentences send out a strong message to the criminals who are exploiting vulnerable people who are too afraid or have been conditioned to believe they are not victims. If you are committing this type of crime, we can and will gather the evidence of your criminality and successfully prosecute you even without a victim complaint.”
DCI Sion Hall, one of the force leads on tackling modern slavery, said: “We have dedicated officers working hard to remove this type of threat from our communities and we will continue to do everything we can to help tackle this awful crime. In Lancashire we are committed to rooting out those individuals who choose to exploit others.
“Anyone who suspects that someone could be the victim of modern slavery or has suspicions about a perpetrator can share information anonymously through the independent charity Crimestoppers on 0800 555 111 or with police on 101. We would urge you to look closer, modern slavery could be happening right in front of you – whether that’s in nail bars, car washes, rural businesses, brothels, massage parlours, or a property in your neighbourhood.”
Police and Crime Commissioner Clive Grunshaw said: “Securing this conviction and taking these dangerous men off the streets is a testament to the excellent work done by Lancashire officers in uncovering this often hidden crime. Victims of trafficking or modern slavery are often scared to come forward for fear of reprisals so to get this result without the victims' co-operation shows the determination and professionalism of the team.
“These crimes are a growing area of demand for the police here in Lancashire which is why I have funded dedicated officer posts to support these investigations. This is vital work and I remain committed to ensuring that the police have the resources to tackle criminal groups like this head on. If you see anything suspicious and want to report it then please contact 101 or Crimestoppers and report your concerns.
There is also a national Modern Slavery Helpline offering confidential help and advice, you can also report information to them on 08000 121 700."