Donna and Vanner Johnson loved watching their boys' unique personalities develop as they grew up.
Their eldest son, who is also called Vanner, always loved books.
His younger brother, Tim, pushed them away in favour of a soccer ball.
Until recently, however, one major difference between the pair was hidden.
The Johnsons, who live in Salt Lake City, Utah, had no idea that a mix-up that occurred a decade ago would change two families' lives forever.
'How did I have a baby with a stranger?'
The Johnsons always wanted several children but struggled to get pregnant after the birth of their first son.
They eventually turned to in-vitro fertilisation (IVF).
After a couple of rounds, Tim was born in 2008.
"We were overjoyed," Donna said.
"He was a beautiful, wonderful baby and child.
"And the boys immediately became fast friends."
Donna was always curious about her family history and, in 2020, the Johnsons took an at-home DNA test to trace their ancestry.
When the results came back, the information listed besides Tim's name did not make sense to his parents.
"I saw Donna as his mum and Vanner [Jr] as his half-brother … and it said, 'father unknown'," Vanner said.
Donna immediately suspected something had gone wrong at the University of Utah's Centre for Reproductive Medicine, the IVF clinic where Tim was conceived.
"How did I have a baby with a stranger?" she asked herself at the time.
"How is that possible? And how would I have not known or had any information that that happened?"
The search for Tim's biological father
Donna and Vanner kept the secret to themselves for a year, telling only a handful of people including Tim's doctor and a lawyer.
The lawyer advised them they were unlikely to face custody issues.
Eventually, the Johnsons decided Tim needed to know the truth; Vanner took him out for ice-cream to break the news.
It took Tim, who was then 12 years old, a couple of minutes to process the information.
"He said, 'Well, actually, I guess I just kind of wonder what I'd look like with your DNA, Dad. With your genes,'" Vanner recalled.
"I probably teared up a little bit because my relationship with my son is awesome — it always has been. And, in my mind, I felt like it was going to go the way it went.
"But my fears were that it could go much differently."
Donna and Vanner asked Tim if he wanted to find his biological father and he said he did.
He then took another DNA test, through a different online service, which matched him with a woman named as a potential "close relative".
From there, the Johnsons scoured public records for any information they could find about the woman or her relatives.
A family obituary revealed she had a brother, Devin McNeil.
An online search of his name led to a blog post he had written with his wife Kelly, which mentioned the couple had gone through IVF at the same clinic, around the same time as the Johnsons.
Vanner tracked down a phone number for Devin, who now lives in Colorado, and spent weeks working up the courage to call him.
When he first reached out, Devin and Kelly were sceptical and thought they had been targeted by a scam.
But after speaking with Vanner, and seeing screenshots of Tim's test results, Devin agreed to take a DNA test, which confirmed the Johnsons' theory.
The McNeils also took their own tests to reassure themselves a similar mix-up had not occurred with their other children.
"So now our kids have a half-brother that they never knew, from 12 years ago," Devin McNeil said.
"And [the Johnsons] find out that Tim's brother, [who] he'd grown up with, is his half-brother. And his dad's not his biological dad, and he's got [another] biological dad.
"It's crazy to go through it all and really try and digest it."
From the outset, both sets of parents decided they would give Tim the power to decide how much or little he wanted Devin to be involved in his life.
When the McNeils told the Johnsons they were planning on visiting extended family in Utah a few months later, Tim said he would like to meet them.
Amid awkwardness on both sides, the two families met for a picnic in a local park.
"We didn't know what to expect. But the kids just adored each other — they played and had fun."
Tim had a list of questions for Devin: How tall was he when he was Tim's age? Did he ever have braces? Who is his favourite athlete?
While those questions were relatively easy to answer, the ones about what happens next are more challenging.
"We've often said there's no manual, no book that someone's given us that says this is how you need to act in this situation, because it's such a unique situation," Kelly McNeil said.
"But we just want what's best for him."
Calls for better regulation of 'wild west' sector
Texas woman Eve Wiley felt sad and frustrated when she first heard about the experience of the Johnsons and the McNeils.
She has spent years fighting for stronger accountability in the US fertility sector after discovering her mother's doctor was her biological father.
Her mother has accused the doctor of using his own sperm without her consent.
He denies any wrongdoing.
Last year, a Californian couple sued their fertility clinic, alleging a mix-up had resulted in them giving birth to a child who was not biologically theirs.
Ms Wiley believes many other cases do not receive public attention, due to both parties involved signing non-disclosure agreements.
"These are people's lives that we are creating and destroying."
The fertility industry in the United States is worth billions of dollars, with tens of thousands of babies born as a result of assisted reproductive technology in the country each year.
The sector is regulated by a combination of state and federal agencies, as well as professional, self-regulatory bodies such as the Society for Assisted Reproductive Technology (SART).
Some experts argue it's a patchwork that leads to poor monitoring, little oversight and a lack of transparency compared to other developed nations.
Ms Wiley described it as the "wild, wild west."
SART president Timothy Hickman disagrees.
He says the existing system mostly works well and that mix-up cases are uncommon.
"I would think they're quite infrequent and they're probably due to human error," Dr Hickman said.
"These are situations where it sounds like embryos may have been mixed up or something like that.
"Every lab should have a way to avoid that with both the witnessing and verification — it takes multiple steps through every twist and turn of the actual IVF process."
Many labs now use barcodes to identify each petri dish and the patient it belongs to, which Dr Hickman compared to wearing a wristband in hospital prior to surgery.
He recommended patients check the certifications of clinics and request as much information from them as possible.
"Saying, 'Hey, have you had any challenges in your lab? If so, what's happened? How, what have you done to correct it?'" he said.
"I think those are all very fair questions… if the patient is looking at several different clinics and wants to know what the track record is."
The Johnsons and the McNeils are in the early stages of taking legal action against their IVF clinic at the University of Utah.
"We love the miracle IVF is," Vanner said.
"IVF gave us something we love very much — and we would never want that taken [away] — but it's also very hard to find out what we found out, in the manner we did.
"Why? How? Who's not paying attention? Because it shouldn't be us to be the ones to have to bring attention to this."
The clinic said it could not comment on cases where there was ongoing litigation but that the safety and care of its patients was its primary goal.
"If patients come to us with questions or concerns about their care, we evaluate our procedures and, if necessary, make changes to ensure the safest, highest quality care is delivered to our patients," a spokesperson for the clinic said in a statement.
Navigating an uncertain path forward
For now, the Johnsons and the McNeils are focused on working together to support Tim as best they can.
The path ahead is unclear, but Vanner does not regret tracking down his son's biological father and bringing the two families together.
"Some professional people said, 'You probably don't even want to contact the [biological] father'. [But] I'm glad we did," he said.
"We're both open to what's best for the kids: What's best for Tim, what's best for their family and for our son as well, our oldest son.
"We're building that and we're continuing to see it flourish … but we don't know long term what that looks like, just that we're taking it day by day."
