ON YouTube there’s a brief documentary, made six years ago, about a teenage rock band in Alabama called the Ackleys. It’s a four-piece, anchored by an irrepressible set of apple-cheeked female twins, Allison and Katie Crutchfield. Seventeen years old, they name-check Fugazi, Guided By Voices and the Velvet Underground as influences and are shown playing accomplished, jangly indie rock in graffitied warehouse spaces.


“I see it going on forever of course,” Allison says of the band, “but you never know.”


So often teenage dreams just become the stuff of adult disappointment.


They’re 23 now, these twins, and even though the Ackleys are just a memory, the Crutchfields have continued, forming one band after the next, building a series of cult followings and arriving at the present moment with gale force. Separately they’ve made two of the year’s best and most affecting indie rock albums: “American Weekend” (Don Giovanni), by Waxahatchee, Katie’s solo project, which was released in January, and the self-titled debut album (on Salinas) by Allison’s band Swearin’, which was released in June.


A couple of weeks ago Swearin’ was playing third on a four-band bill at Union Pool in Williamsburg, Brooklyn — a frenzied show that felt like a headlining set. Swearin’ closed with “Movie Star,” one of its catchiest songs, and when Allison was churning heavily on her guitar, she looked square at Katie, who was watching from the front of the crowd, and smiled madly. The dream was still alive.


“This is the first time we’ve done something serious without each other,” Katie said one recent afternoon, lolling on a blanket with her sister on the southwestern side of Prospect Park, in Brooklyn. It was one of the sisters’ last days in New York before moving, with their boyfriends and band mates, to a house in West Philadelphia with a soundproof basement where they’ll live cheaply while touring and recording new material for their respective projects.


Alison wore a cut-up T-shirt for the Michigan band Procession, and Katie wore a floral dress. Neither is more outspoken than the other, but their methods of communication are different. Allison is the direct one, with a booming voice and an electric presence. Katie is slightly more retiring, speaking more quickly and more quietly but also more insistently. She’s also held onto her Southern accent in a way the peppier Allison hasn’t. When speaking they easily pick up each other’s thoughts, politely waiting for lulls, and when they’re at odds, they warmly but firmly correct each other.


Born in 1989, Allison and Katie are identical twins — mirror twins, actually, which means that some of their features are reversed. As kids they took years of dance lessons and participated in school choir. Katie started writing songs and learning guitar, and Allison learned to play drums. At the age of 15 they booked their first Ackleys show at a warehouse space in Birmingham called Cave9, the proprietor of which helped them release their first album and book their first tour.


The Ackleys ran for three years, releasing one album and an EP. After that band folded, the sisters began a new one, P. S. Eliot, for which they’ve been best known to date, releasing two albums and two EPs. That band overlapped with Bad Banana, another collaboration, and the first one in which Allison wrote some of the songs, and also with King Everything, a Katie side project. Over the years the distribution of work became more equitable, as Allison, who had long been content as a position player, became more adept at songwriting and the guitar and began to move out front. (Two songs on the first Swearin’ EP were written by Katie, but to this day the twins have never written a song lyric together, though they both express desire to work on a musical someday; their parents raised them on a steady diet of them.)