Authorities said a "custody battle" between the two clans play a role in the April 2016 killings.
Four people have been arrested in the 2016 killings of eight family members who ran a marijuana farm, police said.
The murders nearly three years ago of the Rhoden family members were "meticulously planned" and centered on a child custody battle, authorities said. The arrested members of the Wagner family had moved to Alaska but later returned to Pike County, the site of the killings, which were spread over four residences.
George "Billy" Wagner III, 47, and Angela Wagner, 48, and their two sons, 27-year-old George Wagner IV and 26-year-old Edward "Jake" Wagner were arrested on Tuesday. They face more than 80 charges, including eight counts of aggravated murder.
It was not known whether they have an attorney.
The slayings occurred on April 22, when eight Rhoden family members were shot to death in four homes located on the family's farm.
The dead were identified as: Hannah Gilley, 20; Christopher Rhoden, 40; Christopher Rhoden, Jr., 16; Clarence "Frankie" Rhoden, 20; Dana Rhoden, 37; Gary Rhoden, 38; Hanna Rhoden, 19, and Kenneth Rhoden, 44.
They were all in their beds and were apparently shot as they slept, police said. An infant, a 6-month-old baby and a toddler were spared in the slayings.
Victim Hanna Rhoden was the mother of Jake Wagner's child and shared custody of the girl, now 5, according to authorities. She was not home when the attacks were carried out and is now in protective care.
"There certainly was obsession with custody, obsession with control of children," Ohio Attorney General Mike DeWine said at a press conference.
"This is just the most bizarre story I've ever seen," he added, saying it "has been by far the longest, most complex and labor-intensive investigation the Ohio Attorney General's Office has ever undertaken."
Early in the investigation, the Wagner family members said they were friends with the victims and considered them family, according to news reports at the time. Angela, the matriarch, referred to the killers as "monsters."
They have all denied any involvement in the killings.
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