Cousins Daljit Kapoor and Harmit Kapoor, and Davinder Chawla, all three in their 40s, pleaded guilty before their trial at Inner London Crown Court on Tuesday.
They admitted two charges of conspiracy to help asylum seekers from Afghanistan to enter the UK illegally between May and June 2014 and will be sentenced later this month.
"We say these three men are the facilitators in this... organised crime, where they are using genuine British passport holders within the Sikh community.
It's a Sikh conspiracy and it's occurring because it's very difficult for the authorities at the border control to distinguish who's who on the passports," prosecutor Edward Aydin had said at an earlier hearing at Camberwell Green Magistrates' Court.
The passports shown by the Afghans all had photos of Sikhs wearing their turbans and border staff failed to spot the difference.
Around 30 Afghans are said to have successfully claimed asylum after paying the three fraudsters 12,000 pounds per family to enter the UK.
A gang member would drive to Paris with genuine passports of family members and hand them over to the Afghan families so that they could get through airport security.
Once in the country, the gang retrieved the passports and reused them with new families.
Harmit Kapoor also admitted booking flights between June 8 and June 21, 2014, for the asylum seekers to get to Britain and Chawla admitted hiring a vehicle to facilitate their entry into Britain when he drove to Paris.
He had been jailed for his part in an identical crime in February 2011, along with four other men.
Airline staff are believed to have suspected something was wrong and alerted French authorities, leading to the immigration racket being busted.
A fourth suspect, 41-year-old Joginder Dawan, pleaded not guilty to one count of conspiracy to help asylum seekers enter the UK and one charge of assisting the offence by allowing his passport to be used to book flights and travel.
Not guilty verdicts were recorded for both counts and he was discharged.