Joshua “J.J.” Vallow, at left, and his sister Tylee Ryan.

Tylee Ryan and Joshua Vallow

The grandparents oftwo missing Idaho kidsare speaking out, telling PEOPLE they’re holding out hope the siblings will return safely.

But they also have harsh words for the mom of the siblings, who has refused to cooperate with the police investigation into their disappearance.

The two siblings — Joshua “J.J.” Vallow, 7, and Tylee Ryan, 17 — were last seen in September, according to the Rexburg Police Department. Their mother,Lori Vallowhad recently married Chad Daybell, a religious author who writes about prophecy and the end of the world.

Nothing is known about the kids’ whereabouts — or even if they’re alive or dead. But in this week’s issue of PEOPLE, J.J.’s paternal grandparents say that they’re “holding out hope” the kids are alive.

“There are two phone calls I want to get right now,” says Larry Woodcock, the boy’s grandfather. “The first call is that they’ve been found right now. J.J. and Tylee are safe and they’re heading home. And the second call is that Lori and Chad Daybell have been arrested.”

Joshua “J.J.” Vallow, at left, and Tylee Ryan.Rexburg Police Department (2)

Joshua Vallow, Tylee Ryan

No criminal charges are pending against either Lori or Chad, although authorities previously said that her refusal to produce the children would risk civil or contempt of court citations. As of Tuesday morning, there have been no repercussions for failing to produce the kids.

over of people magazine featuring Kate Middleton with the headline “princess Kate gets personal”

• For more on the disturbing disappearance of J.J. Vallow and Rylee Ryan,subscribe now to PEOPLEor pick up this week’s issue, on newsstands Friday.

Larry Woodcock says that Lori’s lack of cooperation is egregious. “She didn’t comply with a court order,” he says. “She belongs in handcuffs.”

Lori Vallow.Rexburg Police Department

Lori Vallow

Want to keep up with the latest crime coverage? Sign up forPEOPLE’s free True Crime newsletterfor breaking crime news, ongoing trial coverage and details of intriguing unsolved cases.

In addition to the case of the missing kids, authorities in several states are investigating a spate of suspicious deaths that have swirled around Chad and Lori in the past few months.

It was during the investigation into Tammy Daybell’s death that police discovered the children were missing.

source: people.com