The family of Harry Dunn will fly back out to the US this week as they continue to pressure the American authorities over their son’s case.
Spokesman Radd Seiger said the family had invited President Donald Trump to meet with them once again and that the offer was being considered.
It comes as the family consider bringing a private criminal prosecution in the UK against the US suspect in the case.
A file of evidence was handed to the Crown Prosecution Service (CPS) on November 1 after Northamptonshire Police interviewed 42-year-old Anne Sacoolas in the US.
Mr Seiger said Mr Dunn’s parents, Tim Dunn and Charlotte Charles, were going through “untold mental anguish” caused by what they call a “delay” in a charging decision in the 19-year-old’s case.
The PA news agency understands that the family have requested two meetings with Chief Crown Prosecutor Janine Smith, who has said she will meet them once a charging decision has been made.
In a statement on Monday, Mr Seiger said it “boggles the mind that no charge has yet been laid” and added that discussions about a private prosecution were under way.
He said: “Sadly, the family are losing faith and confidence in the criminal justice agencies to do the right thing and authorise that charge and have therefore reluctantly concluded that they have no choice other than to now actively consider with their lawyers in London bringing a private criminal prosecution against Anne Sacoolas.
“Those discussions are now well advanced. Frankly, no-one who had been through what they had been through, and are continuing to go through, could blame them.”
Mr Seiger added that the family felt “completely let down and abandoned” over the case, more than 12 weeks after the teenager died in a head-on collision.
In the US the family are separately pursuing a civil claim for damages against the suspect, Mr Seiger said.
Mr Dunn was killed when his motorbike was involved in a crash with a car outside RAF Croughton in Northamptonshire on August 27.
Mrs Sacoolas, the motorist allegedly responsible for the crash, claimed diplomatic immunity and was allowed to return to the US.
A CPS spokeswoman said: “We appreciate how difficult this time must be for Harry’s loved ones and understand that his family are seeking answers.
“However, whilst the case is under active consideration, we are unable to meet with Harry’s family to discuss its progress.
“The CPS is carefully considering all the available information, including the impact on Harry’s family, in order to make an independent and objective charging decision.
“Our Chief Crown Prosecutor will meet with Harry’s parents as soon as is it possible to provide them with an update.”