Harry Dunn's family plan to sue the US government over 'misconduct and a cover-up' following the teenager's death in Northamptonshire.
They also want to take Anne Sacoolas to court after the US diplomat's wife fled the country despite admitting to causing the fatal crash near Croughton in August.
The family from Charlton and Brackley have returned to the US to start legal proceedings with American lawyers, having previously met US President Donald Trump.
Family spokesman Radd Seiger said in a statement: "We are bringing claims against both Mrs Sacoolas in the USA for civil damages as well as the Trump administration for their lawless misconduct and attempt to cover that up.
"No one is above the law and the family are determined to ensure that this never happens to another family again. It will be Harry's memorial. His legacy."
Harry, 19, died in hospital after the crash involving his motorcycle and Mrs Sacoolas' car, which her lawyers said was being driven on the wrong side of the road.
The 42-year-old American initially cooperated with police but then claimed diplomatic immunity before leaving the UK and has so far refused to return.
The family has raised more than £75,000 as they hope to bring her back to Britain, but their campaign has now turned to getting answers from Northamptonshire Police and the British and American governments.
On a awareness-raising trip to the US, Harry's parents Tim Dunn and Charlotte Charles turned down the chance to meet Mrs Sacoolas in the White House during a meeting with the president.
In today's statement, Mr Seiger described it as a "disgusting stunt" and that the family has lost faith in Mr Trump's promise to look at the case from a different angle.
"The Trump administration is not only hell bent on breaking international laws, rules and conventions on diplomatic immunity, but they have no care or concern for the welfare of Harry's family or any real intent on finding a solution," he added.
The Dunn-Charles family also plan to sue the Foreign and Commonwealth for their involvement in Mrs Sacoolas' departure, and have referred Northants Police to the Independent Office for Police Conduct.