Andrew Nay, 39, crashed his Land Rover into the girls' family car as he made a right turn across oncoming traffic on the A509 near Wellingborough.
Katrina Raiba, now six, and her sister Karlina, eight, were left paralysed from the waist down.
The girls' parents said they would "never be able to forgive" Nay.
Live: Reaction to sentencing of Andrew Nay
Northampton Crown Court was told Nay, a Jaguar Land Rover manager and off-road driving instructor, was tailgating and "bullying" a woman who had been driving a Mazda.
To get away from him during his pursuit in October last year, she safely turned right onto the B547 towards Little Harrowden.
Nay, who was seen laughing with his male passenger, undertook a Mercedes and then, in an attempt to follow the Mazda, made an "absolutely ridiculous" turn, the court heard.
He hit the family's Vauxhall Signum that was travelling along the A509 in the opposite direction.
The girls' parents, Roberts Raibais and Renate Raiba, released a statement saying: "Andrew Nay's reckless actions had devastating consequences for our two beautiful daughters.
"Katrina and Karlina were happy, active children and he has robbed them of that.  We will never be able to forgive him.
"Every day they ask 'when will we start feeling our legs again?' They think it's going to get better and it's too hard to tell them."
Nay, from Weldon, Corby, admitted four counts of causing serious injury by dangerous driving, but denied he had been chasing the Mazda prior to the crash.
Judge Adrienne Lucking QC said: "This was a prolonged, persistent and deliberate course of very bad driving.
"No sentence I can pass will ever feel like enough for this family."
The judge told Nay his account of events had been "incredible and inconsistent".
Sgt Tony Hopkins, of the Serious Collision Investigation Unit in Northamptonshire, said: "This is probably one of the most tragic cases that I think I've had to deal with in my career to date.
"There is no end for the family, this will go on for years and this will affect them for years."
He added: "I'm pleased to see that the judge has been able to see through Mr Nay's story, and has been able to see what the witnesses have evidenced to us over the few months, to highlight how long this incident actually went on for."
Jaguar Land Rover' said in a statement: "We are deeply saddened by this terrible incident and our thoughts are with the Raiba family. We can confirm that Andrew Nay is no longer an employee of Jaguar Land Rover."

The site of the Chicago Rock club, on New Street, Barnsley, was badly damaged when a fire broke out last week.
At its height, South Yorkshire Fire and Rescue Service used eight fire engines to tackle the blaze at the disused building.
David Shepherd, Barnsley Metropolitan Borough Council's director for economic regeneration, said the demolition would take place over the weekend.
He said: "We've worked with Historic England to see if anything on the site can be preserved, but unfortunately we've come to the decision the building cannot be saved."
Mr Shepherd added the demolition would take place in order to "ensure people are safe and are not at risk from the building collapsing without any warning".
More on this and other local stories from across Sheffield and South Yorkshire
A driving instructor who left two young sisters paralysed after a "road rage" crash in Northamptonshire has been jailed for four-and-a-half years.
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A former nightclub gutted by fire is to be demolished.