Ahmad al-Saffar, uncle of the girls' mother, said they are in foster care "against their will," and should be raised with family members in a Muslim home.
Iraqi-born Briton Saad al-Hilli, 50, his wife Iqbal, 47, her mother Suhaila al-Allaf, 74, and an apparently unrelated French cyclist, Sylvain Mollier, 45, were shot to death in September.
The al-Hillis' two children, Zainab, 7, and Zeena, 4, survived the shooting, though the elder sister was badly beaten. The youngest child was unscathed after hiding under the bodies of her mother and grandmother.
The family members were shot in a car park while vacationing at a nature preserve in the Alps outside Annecy, France.
When the two girls were returned to Britain, they were placed with a foster family.
They are "deprived of being in an environment which is the same as [provided] by their parents, in regards of religion and culture," said al-Saffar, an uncle of Iqbal.
Al-Saffer also criticized the French investigators because he feels the family's relatives are not being treated as victims, but are being put on trial, Britain's The Guardian reported.
"I think the French cyclist was the target. The mounting evidence and leaks are saying the main target was the cyclist. There is no reason for our family to be targeted in France when they were on vacation," al-Saffar said.
Ballistic tests show Mollier was shot before the family, The Guardian said.