Tayla Alexander, 17, died and her sister Sunmara, 15, suffered critical injuries in the crash on Summit Rd in Christchurch on November 27, 2019.
Sunmara, an Ashburton College student, died later in hospital on December 13, on her 16th birthday.
A teenage boy who was also a passenger suffered serious injuries and survived.
Levi Phillip Fiddymont was charged with two counts of dangerous driving causing death, as well as one charge of dangerous driving causing injury.
He initially pleaded not guilty to the charges, claiming his Subaru WRX's brakes failed on him coming downhill that night.
But part-way through a trial in the Christchurch District Court Fiddymont changed his pleas and admitted all three charges.
Judge Paul Kellar today sentenced Fiddymont after hearing harrowing victim impact statements from the family of the dead girls.
The girls' father Jason Alexander told the Herald after the sentence was handed down: "I am relieved it's over. I'm pleased he didn't get a bracelet, I just wanted him behind bars".
Alexander was the first of five people to read statements in court today.
"Levi when Tayla and Sunmara died I was overwhelmed by grief and wanted to be with them," he said.
"I've had over two years to think what to say to you… I could and would forgive you if this was just an accident… but this was an act of pure stupidity."
He said Tayla had a "heart of gold" and was a kindred spirit with huge plans and dreams for her future.
Sunmara was "a fun-loving kid" who "loved life" and had a "strong will and a strong mind".
"Not only did I lose my two daughters, I lost my two best friends, he said.
Alexander revealed he spent a week in ICU after the crash in an induced coma after he tried to end his own life.
"This has ripped my entire world apart," he said.
"I truly hope you never have to experience yourself the grief and heartache we have been through."
He said he went from the oldest of three to an only child "in the blink of an eye".
"It will never change," he said.
"I had to bury my 17-year-old sister and then I had to sit and watch my 15-year-old sister take her last breath... you did this, this was all your fault.
"I'll never see them flourish, never, all because of your actions."
Tayla's best friend shared her heartbreak at losing her "soulmate".
She has suffered physically, emotionally and mentally and said the pain of losing her friend was "indescribable".
"You have completely destroyed me," she told Fiddymont.
Another friend who had known the girls his whole life recalled the phone call that changed his life forever.
The court process had been "draining".
"Your actions on that day... make me sick to my stomach," he told Fiddymont.
A friend who had known Jason Alexander for 30 years thanked the first responders for their efforts in trying to save the girls and the lead investigator for his work on the case.
"Levi Fiddymont is a name I will never forget," he said.
He said the driver showed "absolutely no consideration" for his passengers.
"You Levi, are responsible for taking Jason's children... because of your reckless actions, he said.
"There is no respect, no remorse... I have watched my best mates go through it all.
"You didn't even show your face and pay your respects (at the funerals).
"The heartbreak you have put on Jason's family is unforgivable... he blames himself Levi.
"You have dragged Jason, his family, his friends through hell and back, taking the life of two innocent girls.
"It can never be undone but you Levi, can take accountability."
Judge Kellar outlined the offending before handing down the sentence.
During the trial the court heard that Fiddymont was likely doing around 110km/h when the car crashed.
Because of his speed, Fiddymont failed to negotiate the first bend and the car crossed the centreline before crashing into the steep rock back.
The car spun anti-clockwise down the bank on the other side and Tayla, who may not have been wearing a seatbelt, was thrown from the backseat.
She struck a steel roadside barrier and landed 28m away, dying from massive head injuries.
The car came to rest 3m down the bank and Fiddymont and the male passenger managed to get out.
But Sunmara, who was seriously injured, was trapped inside the vehicle. It caught fire when the fuel tank ruptured and she received significant burns before emergency services could rescue her, the court heard.
The court also heard Tayla sent a text message to her best friend moments before the fatal crash to say, "Bro I'm going to die tonight".
When her friend messaged straight back to ask why, Tayla replied at 10.54pm: "Haven't gone so fast around Port Hills before".
"OMG Tayla!!!!" her friend replied.
The male passenger, who broke his collarbone, ruptured his spleen, and had a brain bleed, has no recollection of the crash.
Fiddymont's lawyer Andrew McCormick said the crash was tragic and the court case that followed had been hard and harrowing.
He explained why his client changed his plea part way through the trial.
He said after hearing the "complex" expert evidence for the first time in full, he changed his plea "quite appopriately" and took "responsibility for his driving" as soon as possible.
McCormick acknowledged the "brave" statements made in court today.
He maintained Fiddymont was remorseful and had good prospects for the future.
"This is simply not something he has ever taken lightly and he never will," he said.
"Mr Fiddymont has wanted to apologise... since the time it happened."
McCormick said his client was "constrained" by the police investigation and had been advised by friends and family to be "careful" what he said about the crash.
Later on, his bail conditions meant he could not contact the girls' family.
"Mr Fiddymont did not intend harm to anyone that day... he's carrying a huge burden and a heavy cross he will bear.
"Through me, Mr Fiddymont apologises deeply to the Alexander family."
Judge Kellar told Fiddymont that if he had stuck to the speed limit the crash never would have happened.
"And none of us would be here today," he said.
He said he needed to hold Fiddymont accountable for "this most tragic event and deter others from driving the same way in future.
He set a starting point of four years in prison for Fiddymont but reduced that for his youth, previously clean criminal history, and "somewhat generously" his eventual guilty plea.
Further discount was given for his remorse.
Fiddymont was sentenced to two years and four months in prison.
He is disqualified from driving and holding a licence for a period of four years from today.
Earlier today Jason Alexander told the Herald he wanted Fiddymont jailed for his lack of remorse and empathy.
"I think for the crime he has committed he deserves to be put in jail," he said.
"I offered him forgiveness from the beginning but now I feel foolish.
"He never responded and has been arrogant all the way.
"This was no accident, it was stupidity trying to take that bend at high speed on that road.
"There will never be justice, my girls are dead nothing will bring them back and the third passenger has lifelong injuries."
Alexander feels saddened he will miss celebrating his daughters turning 21 and walking them down the aisle.
"I will never have the honour of holding and watching my grandchildren grow up, this has all been taken from me. I have seen the pain and hurt my parents are going through," Alexander said this morning.
-By Anna Leask
