EXCLUSIVE: Aly & AJ on Finally Getting to Grow Up, on Screen and in Their New Music

The sisters also reveal the one song they'll never perform again.

Aly and AJ Michalka are moving forward by revisiting their past.

The sisters co-star in the new dramedy Weepah Way for Now, a somewhat autobiographical movie written and directed by Aly’s now-husband, Stephen Ringer.

“He was always around our house, obviously because we were dating,” Aly, 27, tells ET. “And he was like, 'There's something here that needs to be captured on film, so let's create a movie about your sisterhood and the relationship the two of you have, which is very unique.’”

The film is a love letter to sisterhood and Los Angeles, and delves into tough topics including cancer, mental health, sex and even death.

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“It's a little brave, some of it,” AJ, 25, admits. “It's probably the most adult you've seen us as a pair, which is kind of cool. You know, we've done some past films together when we were kids, but nothing like this.”

“It was a really therapeutic experience for AJ and I, just because we touch on topics that definitely have happened to us in our lives,” Aly adds. “So, the story, some parts are real, some are from our own lives. Some aren't … it’s for the audience to take away their own opinion of what they actually think happened to us.”

The film features original music by the sisters, including one song they recorded as 78Violet, “Boy.” The duo changed their band name from Aly & AJ, the moniker they used while signed to Disney-owned Hollywood Records, to 78Violet in 2009. They only released one song under the new name, 2013’s “Hothouse,” before announcing in late 2015 that they would once again be recording as Aly & AJ.

“We just realized we're Aly and AJ,” AJ says. “Those are our names. That's how people know us.”

“There's nothing that we can hide from,” Aly adds. “I think there was also a moment in finding that new band name where we were trying to separate ourselves from being children, and seen as being as childlike performers. Now, we're writing music as adults and that transition is really hard.”

“There's basically been two records now that have just been hidden on a shelf,” Aly reveals.

“Those are going away,” AJ says. “We're massive perfectionists, and I know it's been a long time coming … This is the year where Aly and I felt inspired, and felt like we can do this, with or without a label. We're going to write this record ... it's time to really start getting back to the roots of who we are, which I really think music is where it all started for us.”

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It’s been nearly 10 years since the duo released their last full-length album, 2007’s Insomniatic.

“We're now speaking about adult things in our songs,” Aly explains, “and the relationships that we've had, or the life experiences that we're now able to bring to our songwriting, which is different than when you're 13 and 15.”

The sisters have penned about seven new songs for their upcoming record, which they expect to release early next year.

“I'd say it's very indie rock, and there's definitely pop sensibilities and pop lyrics, but I'd say that all of our stuff has led with depth,” AJ says of their new sound. “It's all very genuine and very honest, and just a look into our lives.”

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Aly and AJ hope to tour with the new material next year, too -- but if you see them in concert, there’s one song you won’t hear: “Like Whoa.” The track, off Insomniatic, is the one song the sisters say they’ll never perform again.

“It's funny that you can write something, and you were 100 percent into it in the moment, and you're like, I'm 100 percent out now,” Aly confesses.

“I don't like the lyrics,” AJ admits. “I don't like the way the chorus moves. It just doesn't seem like us.”

But don’t worry -- the sisters are still fans of their other hits. Reworked versions of “Potential Breakup Song,” “Rush” and “Chemicals React” will all pop up on future set lists.

“We always really enjoyed performing live because it felt like we were able to take what we had recorded on the album and make it an experience for the fans,” Aly shares.

“It gets a new moment live,” AJ says.

Keep an eye on Aly and AJ’s Twitter and Instagram accounts to keep tabs on all new music announcements. In the meantime, check out Weepah Way For Now, out digitally everywhere -- and see our full chat with the sisters below.