With a nine-piece band that boasts a banjo, a violin and two drummers, the Oh Hellos know how to harness some glorious chaos. “We’re really fortunate to have these really stellar musicians who rise to every challenge we put to them and manage to be wildly energetic and look like they’re going to hurt themselves,” says Tyler Heath, who co-leads the folk-rock outfit with his sister Maggie.

Hopefully the musicians won’t sustain bodily injury—even if they overdo it for the holidays—when the group invades the Paradise Rock Club on Dec. 17 as part of an eight-city tour dubbed the Oh Hellos’ Christmas Extravaganza.

“We bring in the endearing family awkwardness that we grew up with,” says Tyler, 28, noting the siblings had to “perform in front of the whole family, which is now what we do for a living. Everything about Christmas as we were growing up, everything that we felt, enjoyed and endured, we’ll try to share that.”

There’s nothing awkward, however, about The Oh Hellos’ Family Christmas Album, released in late 2013 and repackaged last year but never supported on tour before. “I think we’ve played it live at three shows,” he says, “and one of them was a New Year’s show, which might have been an ill-considered move.”

Most pop acts that offer seasonal tidings tend to play the repertoire fairly straight. But for their Christmas record, the Oh Hellos drew on orchestral ambitions to craft four movements that weave several carols (including “O Come All Ye Faithful,” “Silent Night” and “Joy to the World”) into original arrangements that blend solemnity and exultation. On tour, they’ll contrast those hymns with other Christmas tunes that singer/guitarist Tyler describes as “definitely silly.”

“Everything’s going to feel and look real Christmasy,” he says of a live show to be evenly split between holiday fare and the Oh Hellos’ own originals. Yet perhaps it’s fitting that a group that began in 2011 after the siblings recorded a song for their mother’s birthday would indulge in such a family-centric holiday.

“We did grow up in a musical family,” singer Maggie, 24, says on a joint call with her brother from their home base in San Marcos, Texas, noting that their mother was the daughter of a band director. “We grew up in a very encouraging atmosphere and took piano at an early age, whether we wanted to or not.”

The Heath kids grew up on a ’90s diet of contemporary Christian music (“Because that’s where the car radio was always tuned,” Tyler says). Maggie participated in choir, and they both played in the high school band. But she later fell for the pop band OK Go as well as metal, while he shifted from Christian rap-rockers DC Talk to the quirky pop cult band Tally Hall. And they both became fans of Sufjan Stevens, whose use of banjo in orchestral indie-rock clearly echoes in the guest-dotted The Oh Hellos’ Family Christmas Album.

“One of the big things for me that I like about Sufjan’s music, and specifically the banjo, is that he doesn’t play it in a bluegrass style,” Tyler says. “He plays it like finger plucks. It’s softer and gentler.”

For the Oh Hellos’ own dynamics—which swing from solemn to giddy, from almost a cappella vocals to textural outbursts—Tyler also credits his study of classical orchestral composition. “Those big dynamic ranges, I love that kind of stuff,” he says, “and I’m always trying to bring more of that into the music that we write.”

Perhaps that’s why it didn’t take long for the siblings—who made the Oh Hellos’ 2012 full-length debut Through the Deep, Dark Valley almost entirely by themselves as a bedroom project—to enlist other players, largely to convey the music onstage.

“We thought we’d put that record out and no one would pay attention, and we’d say, ‘OK, we enjoyed that,’ ” Tyler says, calling their growth “incredible.” In more ways than one. Of their current, electric live nine-piece, he says, “The energy shoots through the roof.”

The Oh Hellos’ Christmas Extravaganza plays the Paradise Rock Club on Dec. 17.