The six have now been sentenced for life "for a period of 25 years", the court in Maharashtra state has ruled.
Eight men were found guilty in September 2008. Two were given life sentences. Three others were acquitted.
The Dalits - a woman, daughter and two sons - were killed by an upper-caste mob in a land row. The husband escaped.
The case led to widespread protests. Crimes against Dalits, formerly known as untouchables, often go unpunished in India.
Discrimination against Dalits, who are at the bottom of the centuries-old Hindu caste system, is a punishable offence in India.
But campaigners say violence against Dalits continues.
Raped and murdered
The brutal killings took place on 29 September 2006 in a remote village called Khairlanji, in Bhandara district in the north-east of Maharashtra, western India.
Surekha Bhotmange, her 17-year-old daughter Priyanka and two sons, 19-year-old Roshan and 21-year-old Sudhir, were at home when the mob broke into their mud hut and murdered them.
The four were dragged out and beaten with bicycle chains, sticks and other weapons.
The court heard that the mother and daughter were stripped and raped by the mob. The women's bodies were found in a nearby canal the next day.
Surekha's husband, Bhaiyyalal Bhotmange, managed to escape and hid behind a tree from where he watched helplessly as his family were killed.
He pursued the case with the support of several human rights activists.
The killings led to widespread protests across Maharashtra.
In the traditional Hindu caste system, Dalits were considered the lowest of the low castes.
They were expected to do the most menial jobs in villages. They could not share basic amenities, including drinking water, with upper-caste people.
Such practices still exist in rural areas.
A court in India has commuted to life in jail the death sentences of six men convicted of killing four members of a lower-caste Dalit family in 2006.