The trio are now due at the Old Bailey in London later.
Henry Long, 18, from Mortimer in Reading, and two 17-year-old boys, who cannot be named because of their age, spoke only to confirm their name, date of birth and address.
The hearing at Reading Magistrates' Court lasted just 8 minutes this morning.
The three, along with Thomas King, 21, from Basingstoke, are also accused of conspiracy to steal a quad bike.
The trio charged with murder were remanded in custody by District Judge Davinder Lachher to appear at the Old Bailey later (19/09) for a preliminary hearing.
King, dressed in a green jacket, stood in the well of the court during proceedings and will also appear at the Old Bailey this afternoon.
No pleas were entered at the court, which saw a heavy police presence.
The defendants' family and friends shouted "love you" as the three in custody were led away.
Newlywed Pc Harper, 28, was based at Abingdon station.
He was killed on August 15 near the village of Sulhamstead in Berkshire when he was dragged under a van while responding to reports of a burglary.
He had been married to Lissie for just four weeks when he died.