Burmese pair Zaw Lin and Win Zaw Htun, both 21, have been arrested by Thai cops but claim their confessions to the double murder were beaten out of them.
Now Thai justice chiefs have told the victims' grieving parents they can file joint murder charges against the men and help see them die by lethal injection.
The battered bodies of Hannah, 23, of Hemsby, Norfolk, and David, 24, of Jersey, were dumped on the beach in the sunshine resort of Koh Tao on September 15.
Mr Miller died from drowning and blows to the head, while Miss Witheridge died from severe head wounds.
Thai law allows the families to hire extra lawyers and investigators to get additional evidence to help ensure the murderers are brought to justice.
And prosecutors hope they will fly out to join them to bolster the case.
The men initially pleaded guilty to the allegations but have reportedly retracted their confessions, saying they were made under duress.
They also face allegations of rape and theft as well as murder.
Miss Witheridge's family has also pleaded for the 'right people' to face justice.
In a family statement, just before Hannah's funeral earlier this month, they said: "The past three weeks have been unimaginably difficult and there are no words that can adequately describe the heartache and despair that our family is experiencing.
"As a family we hope that the right people are found and brought to justice."
The Burmese men have admitted they were drinking beer and playing guitars near the murder scene on the night of the killings.
If convicted, they could be given the lethal injection or face death by firing squad.
British cops are preparing to fly out to the island and are expected to focus on securing independent checks on the DNA samples of the two suspects.
