They are charged with committing hate crimes last year for assaulting Amish men of a different sect.
The family members of bishop Samuel Mullet Sr. allegedly forcibly restrained Amish men last year and cut their beards and hair with scissors and battery-powered clippers, injuring the men and others who tried to stop the attacks, according to the Justice Department.
The four women were charged in the attacks in March and are reportedly the wives of Mullet's relatives. The 12 men have all pleaded not guilty.
The attacks carry tremendous symbolism and show the attackers' degradation of the Amish faith, in which men grow their beards after marriage and the women do not cut their hair to adhere to biblical teachings.
According to a criminal complaint against the Mullet family, the attacks reportedly grew out of a religious feud spawned four years ago between Mullet and the wider church.
Mullet, as the head of the Bergholz clan sect of the church, excommunicated eight families who left the sect under his rule. The families reportedly started leaving in 2005 because they found Mullet's behavior controlling.
A 300-member bishops council of the Amish church reviewed his decision and and overruled it.
According to the complaint, Mullet's former daughter-in-law and son-in-law told investigators that he caused physical injury to those who defied him and allegedly "counseled" married women by having sex with them.
Last year, Mullet allegedly traveled with his sons, sons-in-law and nephews to the home of one bishop who had ruled against him. They then assaulted him and his son, pulling and cutting their beards, and took pictures. They then repeated the same attack at another person's house.
Emanuel Shrock also allegedly sent a letter to a fourth victim, asking him to come to Schrock's home in Bergholz, Ohio. When the victim arrived, his beard was cut as well.
The person hired to drive Mullet's clan around reportedly testified against them and five others confessed their involvement to the FBI.
An updated 10-count indictment last month alleged that the men and women had tried to hide or destroy evidence, including a pair of shears and a bag of hair. The indictment also charges Mullet with lying to federal agents when he denied knowing of an October assault.
In October, Mullet told The Associated Press that although he didn't tell his relatives to commit the crimes, he did not stop them from carrying them out.