Aliyah Weekes, 19, of St Mary's Road, NW10, and her 16-year-old friend, instigated the victim’s rape after she was accused of leaking confidential information disclosed to her by Weekes.
The court heard that Weekes believed the victim had “snitched” on her and, in an act of revenge, teamed up with a 16-year-old friend - who cannot be named for legal reasons - to confront the victim.
In April 2013 at a location in Brent the pair explained to the frightened 15-year-old girl that she would be forced to have sex with a group of boys or would have to face violence.
She was then raped by Aliyah's brother Lacquan Weekes, 18, of Lowlands Road, Harrow.
His assault was interrupted by members of the public and the victim managed to get away before she was further attacked.
Detectives from the Mets Sexual Offences, Exploitation and Child Abuse Command launched an investigation after the victim's mother reported the assault on April 29 last year.
Lacquan Weekes, who was 17 at the time, was charged with rape and Aliyah Weekes and the 16-year-old girl - who is now 17 - was charged with aiding and abetting rape.
On Friday, 19 September, all three were convicted at the Old Bailey following a trial.
They were sentenced today, Thursday, 13th November 2014, at the same court.
Aliyah Weekes was handed a total of fours years’ imprisonment and her brother Lacquan weekes was sentenced to five years. Both were also placed on the sex offenders register.
The third teenager, now 17 years who cannot be named, was sentenced to an 18 month rehabilitation order.
Investigating officer Detective Constable, Daniel Pegg, said: "This was a disgraceful attack during which the victim was surrounded, accused of betraying confidence, assaulted and then threatened with further violence if she did not comply with the demands of the group.
"I would like to pay tribute to the victim for her bravery in giving evidence. I hope the sentences handed out will reflect the serious nature of this incident and dissuade others from committing such offences."