POCATELLO, Idaho — Two young LDS missionaries are preparing to leave their missions to return to Idaho after learning their father, mother and two younger brothers died at home over the weekend from carbon monoxide poisoning.

Sister Jensen Parrish, 22, who studied at BYU-Idaho, was in the 13th month of an 18-month calling in the Washington Vancouver Mission as an American Sign Language missionary. Her younger brother, Elder Ian Parrish, 20, was serving in the South Dakota Rapid City Mission, where he was a zone leader working in North Dakota. He was in the 18th month of a two-year call.

Their father Bill Parrish, and their mother, Ross, died Saturday night or Sunday in their Pocatello home with their brothers Keegan, 14, and Liam, 12, according to the Idaho State Journal.

The family didn't show up for a weekly Sunday night dinner with extended family.

Both missionaries were placed on leave by the Missionary Department of The Church of Jesus Christ of Latter-day Saints, family spokesman Craig Parrish said.

Jensen Parrish has a major role in a zone conference on Tuesday morning and asked to stay until the conference ended. She will return home to Pocatello immediately afterward, Craig Parrish said.

Ian Parrish was working six hours from the mission home. He, too, is expected in Pocatello on Tuesday afternoon.

"They've been given the option to go back if they choose to do so," Parrish said. "Their aunts have spoken to them. Both are anxious to come home and unsure what their future holds. They don't need to know that yet. They'll be OK. There will be hard days ahead, but there are a bunch of us here for them."

In fact, the extended Parrish clan meets each Sunday night for a family dinner that generally draws 25-30 people from the families of Bill Parrish and his siblings and Craig Parrish and his siblings. The two men are cousins.

"Every Sunday night this family gets together and plays games and talks," Craig Parrish said. "We're not like all cousins. In our family, we see them every other day. Bill was 11 months younger than me and was born in the house next door. We grew up together and have continued to spend most of our lives together. It's a very, very close family."

When Bill and Ross didn't show up with their two boys on Sunday night, and Keegan didn't answer his cellphone, Bill Parrish's brother-in-law, Brian Curtis, went to check on them with his wife, Bill's youngest sister, Carri Curtis.

"He is an EMT," Craig Parrish said. "He had enough training to walk into that house and know it was dangerous and that he and Carri couldn't stay."

Bannock County Coroner Kim Quick told media outlets that he believes the four Parrish family members died from carbon monoxide poisoning, which kills more than 150 Americans a year, according to the U.S. Fire Administration.

Parrish said he was told the CO in the home was overwhelming enough that workers didn't enter the home until large fans had worked for four hours to clear the air.

He said investigators aren't sure which of several gas-based appliances caused the tragedy.

"There's no reason to think there was any suffering," he said. "They passed out right in the middle of what they were doing."

The family is leaning on its LDS faith.

"The blessing of being a member of the church is that we know families can be together forever," Craig Parrish said. "Elder Parrish and Sister Parrish know that. They've been out teaching it as Mormon missionaries. They know their parents were sealed in the temple and that means they are sealed to their parents and their brothers forever. At the end of the day, it does make a difference."

A local LDS Church leader, stake President Scott Barfuss, said in a statement released Monday afternoon, "We are deeply saddened to learn of the death of the family members of two of the church’s full-time missionaries. We extend our heartfelt sympathies to these missionaries and their entire family as they mourn this tragic loss."

Carbon monoxide, or CO, has been called "the silent killer" because humans cannot see, taste or smell it, the USFA warns. CO poisoning can be caused by faulty furnaces or other heating appliances, portable generators, water heaters, clothes dryers or cars left running in enclosed spaces.

Police are examining the natural gas appliances in the Parrish home to see if any malfunctioned, according to the AP.

Bill Parrish was a dentist on the Fort Hall Indian Reservation. Both he and Ross, who went by Cathi as a child, were alumni of Ricks College (now BYU-Idaho), BYU and Idaho State University.

CO poisoning claimed several lives and sickened large numbers of Americans in incidents over the weekend.

Twin 80-year-old brothers, William and Walter Schofield, died after working on a car together in an enclosed garage in Chehalis, Wash., on Sunday, according to KOMONews.com.

A restaurant manager died, one of his employees remained hospitalized and 26 others were treated and released after inhaling carbon monoxide at Walt Whitman Shops, a Long Island mall, on Saturday night, CNN reported. A leak was found in the flue pipe of a water heater.

Fire officials in Blount County, Tenn., found high levels of carbon monoxide in a home where a 58-year-old woman and her dog died on Saturday, according to KnoxNews.com.

A dozen people and a police officer trying to rescue them suffered CO poisoning in Arcadia, Wis., on Sunday afternoon. The group, which included seven adults and five children, was using a charcoal grill inside the house to keep warm, the Pioneer Press reported.

The USFA listed symptoms of CO poisoning as headache, nausea and drowsiness.

Precautions against CO poisoning can include the use of a CO alarm, regular clearing of vents and annual professional inspections of appliances. Cars should be removed from garages immediately after they are started. Grills should not be used inside homes for heating.

Email: twalch@deseretnews.com