But what she accidentally learned in October of 2012 changed everything they'd ever known: Pam and husband John's now-21-year-old daughter, Annie, wasn't John's biological child, but rather the offspring of a convicted felon who worked at the Salt Lake City fertility center that had helped the Branums conceive nearly 22 years earlier.
"In the moment my mom told me, I was shocked and confused," Annie tells PEOPLE, explaining her reaction after learning the results of what was merely supposed to be a "just-for-fun" DNA test on 23andMe.com. "But at the same time, I didn’t really expect it to terribly change my outlook on life. I know who I am – and who my family is."
Still, she and her family wanted answers. Through her mom's online detective work, and with the help of genealogist CeCe Moore, they found a distant cousin who shared familial DNA with Annie, which led them to the identity of Annie's biological father: Tom Lippert, a technician at the now-defunct Salt Lake City clinic Reproductive Medical Technologies Inc. (RMTI), which was once contracted by the University of Utah.
More concerning: Lippert was a former law-professor-turned-convicted-kidnapper and an alcoholic.
Salt Lake County Jail / AP
The University of Utah believes the sperm switch was most likely an isolated incident. But after the Branums went public with their story this month – nine months after informing the school in April 2013 – the university began offering free paternity tests to concerned former patients who used the clinic while Lippert worked there between 1986 and 1995.
"We cannot rule out any explanation at this point, which would include possible mishandling of lab specimens," a university spokeswoman tells PEOPLE. "Because RMTI is no longer in business, and because Mr. Lippert is deceased, there is no way to determine if this was an accident or intentional."
The CluesThe Branums are speaking out to warn other people – especially unknowing half-siblings who could potentially be in romantic relationships – after piecing together information from Lippert's past, and after forming an unlikely alliance with his family.
Lippert's widow Jean, 74, who never had children, says her husband told her before his death in 1999 from cirrhosis of the liver that he was a sperm donor with "children out there."
Jean believes the Branums' theory that Lippert could have intentionally been using his own semen to impregnate unsuspecting women for years (the University "will neither confirm nor deny" if Lippert was a registered sperm donor because of privacy concerns, says a spokeswoman). "Oh yes, definitely I believe he could have done that – because of the type of person he was," Jean tells PEOPLE. "He wasn't an honest man. He didn't care about other people. He only cared about his own needs and wants. I think it was probably an ego trip for him."
Pam is still haunted by conversations she had with Lippert when she and John visited the clinic in the early '90s.
"I remember that behind [Lippert] at the front desk was a wall covered with dozens of pictures of babies, his wall. He was boastful about it. He would say how those were the babies he'd helped couples have," Pam recalls. "He was so confident. He gave me confidence that we'd be successful. After Annie was born I even remember thinking, 'I should run one of her baby pictures over there for his wall.' Now, I'm so thankful I never did."
How They're CopingDespite their shocking discovery, Annie, an astrophysics major at the University of Texas San Antonio, says she's never questioned her connection to John.
"Just because my dad isn't my biological father doesn't mean that he's not still my dad," she says. "He's the one who raised me and I know he loves me the same through all of this, and I love him the same. Nothing can change that."
Although questions remain, John and Pam say they have also made peace with their discovery.
"Annie is the biggest blessing we have," her father John tells PEOPLE. "I'm not going to let myself get sick over this, not let that man steal our joy and my health. This whole thing has only brought us all closer."
Pam feels the same way. "In regular circumstances, you would never have these weighty conversations, and we've really had to bare our souls to one another," she says. "You don't want this to happen to anyone, ever, but I have to acknowledge we wouldn't have Annie if this hadn't happened to us."
For more information, go to Pam Branum's website. For free testing, go to the university's website or call 801-587-5852