The 15-year old girl and 14-year-old boy are jointly accused of murdering Elizabeth Edwards (49) and her youngest daughter Katie Edwards, just 13, whose bodies were discovered at their semi-detached home in Spalding in April.
No pleas were entered to the charges and both teenagers spoke only to confirm their names and that they understood the proceedings.
The pair, who cannot be identified because of their ages, sat in the glass-panelled dock of court room number one at Lincoln Crown Court divided by staff but regularly looked at each other during the hearing, which lasted just over 30 minutes.
The boy, who was wearing a black jacket and white shirt, sat clutching a book during the hearing.
The girl, who who was 14 at the time of the alleged offences, sat quietly wearing a black hooded top and trousers, with her head tilted forward.
Both face two charges of murdering Elizabeth Edwards and Katie Edwards on April 15.
The judge, Mrs Justice Carr, who sat without robes, explained the proceedings to both children after Peter Joyce, QC, for the prosecution, outlined the progress of the case.
Representations were also made by Andrew Stubbs QC, representing the girl, and Simon Myerson QC, representing the boy.
The case was adjourned until September 5 when the two teenagers will appear at Nottingham Crown Court for a plea and case management hearing.
If the case goes to trial it will be heard at Nottingham Crown Court on October 5 and is expected to last two weeks.
Both teenagers were remanded in to secure youth accommodation until their next court appearance.
The bodies of Elizabeth Edwards (49), known as Liz and her youngest daughter Katie (13) were found at their home in Spalding on April 15.
Lincolnshire Police arrested the two 14-year-old youths following the discovery and charged them with murder.
A broken window could be seen at the front of the semi-detached property on Dawson Avenue, Spalding.
Liz, who was a regular church goer, worked as a midday supervisor at a nearby primary school and lived at the house with her two daughters. She also has a third grown up daughter.