Department of Corrections records show Mann was released on parole in June.
Myers' son, Isaiah Smith, was away when he heard what happened to his mother, brother and sister - and said he feared for his own life. Both men have public defenders.
Troy police Chief John Tedesco called the killings "an act of savagery".
Tedesco said police arrested the men at 9:50 p.m. Friday without incident at 627 Hamilton St., Schenectady, where Mann lived.
They have been remanded to Rensselaer County Jail without bail.
The day after Christmas, police found the bodies of 36-year-old Shanta Myers, two of her children, Shanise Meyers, 5, and Jeremiah "JJ" Myers, 11, and her partner, 22-year-old Brandi Mells, inside a basement apartment in Troy, New York. He declined to say what kind of device. "The emotions of a police officer are something you repress because there is a job to be done", Tedesco said, adding that no one involved in this case will ever forget it. Police are now asking the public for any information they may have about the killings. He thanked numerous agencies involved and the public for providing tips.
Law enforcement was investigating the deaths as homicides.
"They have suffered an unspeakable loss", Abelove said.
Told the teen via the Times Union, 'I'm not sure if they're coming for me next.' .