They said Michelle died first, and David died before he could be airlifted to Australia for treatment.
Family members said the couple - a former Air Force veteran and former student athlete - were "very physically fit".
'Nobody is telling me what was the cause of the death and that's very hard for me, ' he said.
In an attempt to find Zooey, Calanog said she called numerous local dog kennels and posted about her on social media until she was successful in reuniting with the pup.
Lockheed Martin spokesman Kenneth Ross confirmed with the Fort Worth Star Telegram their bodies have not been transferred to the United States yet and the company is "working with the family" to determine how to "support repatriating them".
Fijian media outlet FBC News reported post-mortem results confirmed the deaths were the cause of an illness, and that samples have been sent overseas for further testing. The couple, who liked to get away once a year on trips where it was just the two of them, had left their 2-year-old son and David's daughter from a previous relationship in the US.
The State Department spokesperson told ABC News it was monitoring the local investigation.
The Health Ministry has put in place necessary public health measures following the death of two American citizens in Nadi over the weekend.
The U.S. Embassy in Fiji would not comment on the deaths but confirmed the Fijian government had issued a warning about a unsafe flu season that was affecting the region.
The couple's remains can not be returned to the United States until a cause of death is determined, according to Calanog. If it is, she said their bodies will have to be cremated.
While their families have been told that they died, they remain in the dark about what caused their sudden deterioration of health. "We know Michelle and David are with us in Zooey".