The Da Silva family likes to be called the "Hexa" in a nod to Brazil's bid to become "hexachampions," which would extend the country's record haul of World Cup titles.
The Da Silvas, who live in the capital Brasilia, see themselves as a sort of talisman, with 14 of them who can raise six fingers on each hand.
"We have more fingers to cross and bring luck," said Ana Carolina Da Silva, a mother of three. Only one of her children, her oldest son, inherited the family trait.
They say they are proud of their extra digits. Some family members also have extra toes.
"For us it's an advantage. Because we were not born with five, we live normally like this. For example, I type with six fingers," said Carolina's sister, Silvia.
All the children wear the Brazilian team's yellow jersey, with their names printed on the back.
"If only the (national team players) knew how many fingers are applauding for them," Silvia said.
The Da Silvas, who are originally from the northeastern state of Maranhao, planned to have a big party on Monday for Brazil's final group game against Cameroon.
Silvia's father, Francisco de Asis Carvalho Da Silva, was known as "Mister Six" and played the cavaquinho, a small four-string guitar used to play samba.
"My father was so proud of having six fingers that he passed on this energy to the family. My brothers who were born with five fingers are the ones who feel different," she said.
When a woman in the family becomes pregnant, the first question relatives ask after the ultrasound is not "what's the sex of the baby?"
"The question is: Does it have five or six fingers? If it's six, we celebrate," Silvia said.
She said her kids shrug off kids who tease them at school.
"We are proud of being called 'six fingers.' Those who want to make us uncomfortable end up frustrated," she said.
- 'John Six' -
Silvia's father founded a club that broadcast Brazilian music in the capital and their descendants have take advantage of their extra digits to become guitar virtuosos.
Her son, Joao, also plays the guitar and studies music in his free time. His extra digits also give him an edge playing video games. His friends call him "John Six."
"My friends always joke about this but we like being called 'six fingers.' It helps a lot in video games," the 15-year-old said.
Some of the women in the family, however, have had operations to remove extra toes to be able to wear sandals.
When they have to give fingerprints, the thumb and the "first index" are made in the same space.
Doctors have explained that their extra finger is due to a genetic mutation, but the Da Silvas prefer not to get into those details.
"Otherwise they will want to study us," Silvia said. "We are happy this way."