Joely Fisher’s feature directorial debut is a true family affair. Her sister, Tricia Leigh Fisher, worked on the original script, and their children read it through to make it as authentic as possible.

Well, as authentic as a story about teens searching for their parents amid magical and mystical elements can be.

“Our life is a project together,” Joely Fisher said in a recent phone interview. “We are cheerleaders for each other. We champion each other … it’s a joy to have somebody who delivers and who’s family.”

Daughters of actors Eddie Fisher and Connie Stevens, the Fishers—half-sisters to actress and script doctor Carrie Fisher and director and producer Todd Fisher—have collaborated on ideas since they were kids. Professionally, they’ve both acted on the television shows Ellen and ’Til Death. Joely Fisher, also an acting veteran of Desperate Housewives, Last Man Standing, and Modern Family, even directed her sister on ’Til Death.

But Oliver Storm and the Curse of Sinbad’s Treasure, set to begin filming in January, will be the first movie they’ve created together on the big screen.

“This is kind of a dream come true for us,” Tricia Fisher said.

The two came across the project after Joely Fisher—who has also directed the Disney Channel show K.C. Undercover—expressed interest in directing a feature to Daemon Hillin, producer of By the Rivers of Babylon. Fisher co-stars with her mother and Crispin Glover in the Southern gothic thriller, scheduled for release next year.

Hillin offered her the initial script about Oliver, an introverted whiz kid who treks through Thailand with his sister, River, to find their missing scientist parents, encountering mysterious forces along the way.

The idea reminded her of films like 1985’s The Goonies that she and Tricia had enjoyed as children. She enlisted Tricia for a rewrite, drawing on their experiences as moms of teenagers and their own sibling dynamic.

“When we read it aloud, we would catch each other on what’s honest and what’s not,” Joely Fisher said. “Without ego, [Tricia] would make changes.”

Tricia Fisher has written scripts since her 20s, but is best known for acting. In recent years, she’s appeared on the TV shows The Mentalist, Criminal Minds, and Rizzoli & Isles. She shares screenwriting credit on the film with Gordon Bressack (The Adventures of Raggedy Ann & Andy, The Electric Company) and James Cullen Bressack (Pernicious, If Looks Could Kill).

“We could play it out as sisters and play it out as actresses, and keep pushing each other to make it better and better,” Tricia Fisher said. Their children also did a table read, which helped highlight which jokes landed and other issues. “They had their input, too.”

The end result has a “tremendous amount of heart,” plus distinct arcs and clear points of view for all the characters, as well as a strong environmental message, Joely Fisher said. “It’s something the whole family can enjoy,” she added, noting with a laugh, “I have five kids. I’ve sat through a lot of movies where I took one for the team.”

The project will shoot in Thailand and is produced by MWM Media Group and Thailand-based Benetone Films. In addition to Hillin, Tim Marlowe is producing, with Rachvin Narula, Kulthep Narula, and Joely Fisher as executive producers. They think Oliver’s adventure “has the bones” of a trilogy, a book, and a videogame, Joely Fisher said.

Although certain that Tricia would say the experience was “intense and crazy,” Joely Fisher said she was proud of her. Joely Fisher’s memoir, Growing Up Fisher: Musings, Memories, and Misadventures, will be released in November, and she empathizes with the writing process. “You’re very vulnerable when you put yourself out there … but why not do it?”

Tricia Fisher teased that her sister is “a born director. Since she came out of the womb, she’s been telling everybody what to do.”

But seriously, folks … “She always wants to get the best, real performance,” Tricia Fisher added. “She definitely has the spirit and energy of someone who was born to do this, and the love and the enthusiasm.”

As a writer, Tricia Fisher has her own rituals: “I tend not to want anyone to read it until it’s at a certain point.”

Although “I can’t imagine not using Final Draft” when pulling all the pieces together, she likes the “different brain connection” of using a pen or whatever’s available for notes and outlines.

“Some of my best ideas I’ll write on an envelope in my car with a lip liner,” Tricia Fisher said. “Some of it, I don’t know where I’m going and just mentally put one foot in front of the other. As long as I keep moving, I’m good.”

As a director, Joely Fisher said she can’t help but be inspired by Wonder Woman. Directed by Patty Jenkins, the film has earned favorable reviews and more than $620 million worldwide since its early June release; it’s on track to become the top-grossing live-action film from a female director, the BBC reports (http://www.bbc.com/news/entertainment-arts-40398892).

“I sat there with my three daughters and loved it. It makes me proud to be a woman and a filmmaker,” Joely Fisher said. “I feel like the way has been paved … in this genre, I’m blessed, and the bar has been set very high.”