Identical twins Briana and Brittany, 35, married identical twins Josh and Jeremy Salyers, 37, and now they're introducing the world to their babies, who are so genetically similar that the cousins are more like brothers.
"You've heard the term Irish twins and you've heard identical twins and fraternal twins," Briana Salyers told TODAY Parents. "But we have quaternary twins."
Related: Identical twin sisters, who married identical twin brothers, both announce pregnancies
The Salyers are parents to Jett, who turned 1 in January, and Jax, who will turn 1 in April, and the cousins share more than the same first initial. Their unique situation makes them genetic brothers.
"They were born to identical twin parents less than nine months apart," Brittany Salyers explained. "Twins married to twins who both have babies at the same time."
Since identical twins share the same DNA, the children of two pairs of identical twins are legally cousins, but genetically more similar to siblings.
The sisters shared they had both discussed the possibility of quaternary twins.
"We were hoping that we would have overlapping pregnancies so that this would happen. We thought it would be really cool," Briana said. "There’s only 300 quaternary marriages known in the history of the world."
The couples, who share a joint Instagram page, posted the interesting scientific fact alongside a photo of the young boys side-by-side.
"Jett and Jax: Cousins, Genetic Brothers, and Quaternary Twins!" the caption read.
The couples married in a joint ceremony at the 2018 Twins Days Festival in Twinsburg, Ohio. Brittany and Briana met Joshua and Jeremy at the Twins Days Festival the year before and their fairy tale weddings were captured on camera for TLC.
Both families live under one roof in Virginia and run a wedding venue site together.
"It was something we all four wanted and when we got engaged, we all wanted it that way," Brittany told TODAY of the unconventional living arrangement. "It’s something that's very nice. (Josh and Jeremy) understand the twin bond like we do. We get to have a lot of together time."
Sharing their compelling journey online doesn’t come without negative commentary for the families.
“We try to ignore sociopathic stalker comments and just focus on the positive,” Brittany said. “Some people think we are really strange and others think it’s really amazing. We’ve gotten a lot of support and interest and we’ve been grateful for that.”
As for future babies, the couples are undecided.
"We are debating if we should go for one more pregnancy each or not," Briana said. "We will make a decision pretty soon. The babies are still pretty young (and) we are trying to wait a little longer to see what to do."