The family was beaten to death with sticks, iron rods and chains, and their bodies were dumped in a canal. The woman's husband was the only survivor in the attack, said prosecutor Ujjwal Nikam.
Discrimination based on caste - the complex social system that divides people into hundreds of groups defined by livelihood, class and ethnicity - has been outlawed for more than half a century in India.
But it remains pervasive, particularly in rural India where people from lower castes are often barred from using upper-caste drinking wells, kept out of temples and denied spots in village schools. Ignoring the prohibitions is often met with violence.
The murder case drew widespread attention after complaints from Dalit groups about the slow pace of the investigation.
"This is a key judgment because it sends a very strong message that brutality, especially to low castes, will be dealt with very strictly," said Nikam.
Defense attorney Sudeep Jaiswal said the men would appeal the verdict.
"The death penalty is for the rarest of the rare cases and certainly does not apply here," he said.
The court acquitted three others for lack of evidence against them.
