Mr. Peretti, 43, a founder and the chief executive of BuzzFeed, said: “It’s a massive relief that it’s really good. If Jordan had done a terrible movie, it would have been really awkward.”
It was a sunny Saturday in February and, after spending the morning at the Broad museum downtown, the Peretti siblings headed to the Elite Restaurant, a dim-sum hot spot in Monterey Park, a suburb, where the similarities and differences between the siblings were on display.
Mr. Peretti prefaced his order by explaining that he is a pescatarian vegan, or “sea-gan.” Ms. Peretti, who is expecting her first child, joked about indulging her pregnancy-induced cravings (“last night a Philly cheesesteak happened, so um … yeah”) and ordered a panoply of shrimp dumplings, sticky rice in lotus leaves and chicken feet, which arrived in a savory sauce she wanted Jonah to try.
“Just take a finger of it,” she said, pushing a dish across the table to him. “Dip your finger in. The sauce is really good.”
She is the little sister. She was a writer for the NBC show “Parks and Recreation,” is a regular on the Fox comedy “Brooklyn Nine-Nine” and is the executive producer of a series based on the Twitter sensation Joanne the Scammer.
He is the big brother. As a founder, also, of The Huffington Post, he has shown acumen for building businesses around viral content and memes. (Earlier this week, and many weeks after this brother-sister date, rumors spread around the web that BuzzFeed plans to raise money through an initial public offering. Carole Robinson, a spokeswoman for BuzzFeed, declined to comment.)
Mr. Peretti, his wife, Andrea Harner, and their twin sons moved to Los Angeles in 2015. The siblings are making the most of the proximity. They share meals regularly, with their spouses and otherwise. They screen movies. They even tried a group game of “Dungeons & Dragons,” an activity usually exclusive to Ms. Peretti and his sons. And they spent Thanksgiving together — Mr. Peretti prepared the meal using only foods available during the Pilgrims’ time — though not Christmas or Hanukkah. “We did a sort of gift exchange,” Ms. Peretti said. “Well, I gave gifts to Jonah. Jonah never gives gifts to me. Go ahead, defend yourself.”
He began to say, “There are some things that are private that I’d rather not talk about …” when his sister piped back in.
“Actually he did give me a 23andMe genetic test,” she continued. “I’m like, are you trying to say we’re not related?”
Their shared sense of humor should put that idea to rest. Although Ms. Peretti is hipper and droller, and Mr. Peretti is geekier, their wit binds them.
They were raised in Oakland, Calif., where they split time between their mother, a schoolteacher who once was on the faculty of the University of California, Berkeley, and their father, a criminal defense lawyer and painter who made museum visits a staple of their childhood.
During their visit to the Broad, after passing works by Chuck Close, Richard Diebenkorn and Takashi Murakami, they approached Richard Prince’s “Eat, Sleep and Drink,” a canvas silk-screened with the sentence, “I eat politics and I sleep politics but I never drink politics.”
Mr. Peretti then pulled up the front of his hoodie to reveal the T-shirt he was wearing. It was emblazoned with the BuzzFeed logo and the words “Failing Pile of Garbage” — the description Donald J. Trump, then the president-elect, applied to BuzzFeed after its news division published a controversial dossier alleging ties between him and Russia.
“I wrote an email to Ben Smith,” Mr. Peretti said, referring to BuzzFeed’s editor in chief. “I was like: ‘What’s the difference between Ben Smith and Busta Rhymes? One likes to “Pass the Courvoisier” and the other likes to publish a dossier.’”
With a wince, his sister replied: “Oh, boo. No you didn’t. Can I ask for that to be off the record?”
Teasing is and always has been an integral part of Jonah and Chelsea’s dynamic, and despite a few obligatory slap fights in their youth (“Jonah’s four years older so he had the upper hand, literally,” Chelsea said), they said it had always been affectionate.
“I want to try to do stand-up,” Mr. Peretti announced during the afternoon jaunt. “And have Chelsea sit on stage critiquing me.”
“Can you imagine?” Ms. Peretti said, laughing.
“Also, I’m starting a new venture at BuzzFeed called Peretti Comedy,” he went on. “And no, she’s not going to be involved in any way. I just figured the name Peretti would be a good one.”
Ms. Peretti countered: “I’ll just go over to Peele then, and leave the family behind.”
“You’d betray the family name?” the brother asked.
“If I get betrayed by the family,” the sister replied.