(CNN) The brother of the stepfather of two missing Idaho children released a statement asking for him to "come forward and cooperate with police."
Chad Daybell and his wife Lori Vallow, the children's mother, left the state. Vallow has refused to cooperate with authorities, police said in a statement on December 30. The children, Joshua "JJ" Vallow, 7, and Tylee Ryan, 17, have not been seen or heard from since September.
Daybell's brother, Matt Daybell, said in a statement to CNN affiliate East Idaho News Friday that he has not been close to Chad Daybell since they were children.
"My immediate family has had little association with Chad the last many years due to our concerns with his religious claims and particular books he had chosen to publish, including his own," Matt Daybell's statement read. "I plead again for Chad to come forward and cooperate with the investigation so that this very difficult situation might be resolved."
Matt Daybell said in a statement Friday he has neither seen nor directly spoken to his brother since the memorial of Chad Daybell's previous wife in October.
JJ's biological grandparents, Kay and Larry Woodcock of Louisiana, held a news conference last week in Idaho to offer a $20,000 reward for information on the whereabouts of JJ or Tylee Ryan.
Kay Woodcock made a public plea to their mother.
"Please, just let us know where the kids are," she said. "It's not difficult. It will end all this, as far as the kids are concerned."
The children's disappearance is part of a complex past 12 months for the family -- a time frame in which police have investigated two deaths, one of which authorities say still is under investigation.
Police determined the children were missing in late November -- four months after Lori Vallow's estranged husband was shot dead in their former home state, Arizona, and shortly after Vallow moved with the children to Idaho and remarried.
Vallow's estranged husband was shot and killed in July during a fight with Vallow's brother. According to a petition for dissolution of marriage filed in February, Vallow's former husband said Vallow "recently become infatuated and at times obsessive about near death experiences and spiritual visions."
Police conducted a welfare check for JJ -- Vallow's adopted son with her late husband -- on November 26 at their home in Rexburg, Idaho, after relatives raised concern about not hearing from him since September.
During the welfare check, both Vallow and her new husband, Chad Daybell, told investigators the boy was staying with a family friend in Arizona, police said.
But police determined that he wasn't staying with a family friend. When police returned November 27 to execute a search warrant, investigators determined Daybell and Vallow had fled the home, and also didn't appear to have taken JJ with them, according to authorities.
Investigators learned that Tylee hadn't been seen since September, though she'd most recently lived with Vallow and JJ in Rexburg.
The case is complicated further by the death of Daybell's previous wife, Tammy Daybell, in Idaho in October. Her death initially was believed to be natural, but Rexburg police announced last month that it was suspicious, and her remains were exhumed.
Daybell and Vallow married a few weeks after Tammy Daybell's death, police say.
Rexburg police have said they're investigating whether that death and the kids' disappearances are connected.
Investigators don't believe the children are with Lori Vallow, but they think she knows where they are or what happened to them, Rexburg police said.
An attorney for the family, Sean Bartholick, released a statement to East Idaho News on December 23 saying that while he is in contact with Vallow and her husband, Chad Daybell, he does not have information about the children. CNN has made multiple attempts to reach Bartholick but has not received a response.
Chad Daybell had connections to a website called "Preparing a People," a religious content provider that describes itself as "as series of lecture events focusing on self-reliance and personal preparation," featuring several Latter-Day Saints speakers.
Publishers of the site, Michael and Nancy James, released a statement December 26 emphasizing that while Daybell, and to a lesser extent Vallow, were featured in the series, neither was an owner or a founder.
Michael and Nancy James said they decided to pull content featuring either Daybell or Vallow in light of Tammy Daybell's death and the disappearance of the children.