The grandparents of a 7-year-old boy who disappeared with his half-sister two months ago offered a $20,000 reward on Tuesday and appealed for the children’s mother—who ran off with a doomsday writer—to reveal what she knows.

Larry and Kay Woodcock traveled from their home in Lake Charles, Louisiana, to eastern Idaho in a desperate hunt for information about Tylee Ryan, 17, and her younger sibling Joshua “J.J.” Vallow.

“We don’t say the ‘D word,’” Larry Woodcock said at a press conference. “We don’t want to and we’re not going to because we truly believe and we hope and pray these kids are alive.”

The whereabouts of Tylee and J.J. are the focus of a federal and state investigation that has expanded to include the death of their mother Lori Vallow’s previous husband; the death of her new husband Chad Daybell’s first wife; and several other sinister incidents.

The Woodcocks expressed bewilderment and fear as they recounted the bizarre tragedies that have befallen the extended family in recent months.

In July, Kay’s brother, Charles Vallow, was shot dead in Chandler, Arizona, allegedly by his wife Lori’s brother, Alex Cox. Cox, who claimed the shooting was in self-defense, has since died under unknown circumstances, leaving Tylee and J.J. as the only other witnesses.

The couple said they didn’t buy the explanation of the shooting because Lori had threatened Charles in the past. “We knew immediately that was wrong,” Kay said. “It was a setup.”

The Woodcocks used to be in constant contact with J.J., who is on the autism spectrum; he is their biological grandson and was adopted by Charles and Lori. But after Charles was killed, they only had three short Facetime conversations with the happy little boy and felt the last one, on Sept. 23, was being monitored by someone.

“We don’t know why we weren’t allowed more access to him,” Kay said. “That was very concerning to us.”

The next strange episode occurred Oct. 2, when the ex-husband of Lori Vallow’s niece says someone driving Charles Vallow’s car shot at him and missed his head by inches in Gilbert, Arizona. Brandon Boudreaux says that before the shooting, his ex-wife had gotten mixed up with the same doomsday group that Lori and Chad Daybell were with and left him.

On Oct. 9, Chad Daybell's first wife, Tammy, reported to Idaho police that she was ambushed in her car by a masked man who pointed a paintball gun at her and then took off when she called for help. “There wasn’t anything there at the time we could do and everybody kind of summed it up as a prank,” Fremont County Sheriff Len Humphries told the East Idaho News.

But 10 days later, Tammy Daybell, a 49-year-old librarian, was dead. Her husband declined an autopsy and police put it down to natural causes.

“My deputies responded and, as we do with most unattended deaths, they took pictures, they looked it over and contacted our detectives,” Humphries told East Idaho News this week. “The detectives had a few questions, they satisfied those, got the information they needed and didn’t see anything that alarmed them.”

Just weeks later, Chad Daybell, 51, married Lori Vallow, 46. The two were contributors to an end-times website called Preparing a People, and Chad had also written a series of books about doomsday and near-death scenarios for a Mormon audience.

By Thanksgiving week, relatives had stopped hearing from the children and asked Rexburg, Idaho, police to check on them. Chad told officers that the kids were in Arizona—a lie. When police showed up with a warrant the next day, the newlyweds had already skipped town.

Last week, police said the couple was not cooperating with their search for the children, who were described as being in “serious danger.” They got a warrant to search the house and seized 43 items, including journals, police said.

The Woodcocks said with each new revelation they have been “blown away” even though they had seen a major change in Lori in recent years.

“Lori was a good mother,” Larry said. “When J.J. was young you couldn’t ask for a better mother. She loved J.J., she loved Charles. I don’t know what caused this conversion.”

“You don’t go from being mother of the year… to the person that won’t even tell you where they are at.”

Through a local attorney, Chad Daybell and Lori Vallow have denied wrongdoing but have also declined to say where Tylee and J.J. are now.

Larry Woodcock said he’s hopeful that the reward will encourage someone else to help solve that mystery.

“We’re asking the public: Please for God’s sake, please, please step up,” he said.