On the big screen, people trudge through a snowy forest carrying a sack of potatoes that will feed many more mouths than its size intends. Later, they steal guns for protection and blow up railroad tracks to derail the Nazis’ plans.

In the audience sit people for whom these scenarios are not fiction. These moviegoers have wrinkled skin and white hair, but decades ago, during World War II, they were optimistic teenagers with a will so unbreakable they were able to survive against all odds in the forests of Eastern Europe.

They were Jewish partisans.

Their story hits the big screen this month with “Defiance,” which opens in the Bay Area and nationwide Jan. 16. Directed by Hollywood filmmaker Edward Zwick, “Defiance” tells the story of brothers Tuvia, Zus and Asael Bielski, three of the 30,000 Jews who escaped Nazi ghettos and camps to form or join resistance groups. The Bielski Brigade, as it was known, saved the lives of some 1,200 Jews.

The Bay Area is home to a handful of former partisans, including sisters Sara Rosnow and Mira Shelub and their brother, Morris Rosnow.

The three were in the audience Dec. 3 at an advance screening of “Defiance” in San Francisco for former partisans and other members of the Jewish community. The screening was co-sponsored by the S.F.-based Jewish Partisan Educational Foundation, which served as a resource for the filmmakers.

Sisters Rosnow, 83, and Shelub, 86, along

with their 81-year-old brother, survived the forests of Poland for two years. The siblings were not in the Bielski Brigade, but met the brothers when their groups’ paths crossed for a month or two toward the end of the war.

Their stories of resistance, strength and hardship are different, but parallel to those of the Bielski brothers.

“At moments it was difficult to watch the movie because I was sitting next to my brother and to my sister’s son, and when there was a big explosion I jumped every

time,” said Sara Rosnow, of Walnut Creek. “There was a lot of killing. And I had to cry. It was a hard thing.”

Said Shelub, “The movie reminded me of my own experiences and triggered memories. I liked it. I thought it was a good portrayal, really. But it is a movie, and certain elements are not real.”

For example, in “Defiance” the partisan group led by the Bielskis is depicted as being extremely organized — everyone is given a specific job to do, and the group is quickly able to set up an impressive infrastructure.

“The forest was very difficult, but it wasn’t [as] orderly” as the movie portrays, Sara Rosnow explained. “My God, [the Nazis] were standing over our heads, waiting to kill us — how can it be so organized?”

Yet the film “captured moments and presented [our story] in a symbolic way,” she added.

The three siblings grew up in eastern Poland in what is now Belarus. The family was forced into a ghetto in 1942.

Rumors quickly spread throughout the ghetto about mass exterminations of Jews, and the residents began to build hiding places to store food, medicine — and themselves.

When the ghetto was liquidated, Sara, Mira and four other young girls hid behind a fake wall in a shed. They stayed there for three days and two nights; their parents and brother were in a different hiding spot.

“They didn’t know whether we were alive, we didn’t know whether they were alive,” Sara Rosnow recalled.

When the sisters emerged in the middle of the night and found no signs of life (everyone else had been discovered and sent to Dvorets, a labor camp in Belarus), they decided to go there as well. They felt like they had nowhere else to go, Rosnow said.

“We came into the entrance, told them where we were coming from, and they let us in,” she said. “It doesn’t sound very reasonable, does it? But the whole thing was not very reasonable.”

Mira and Sara reconnected with their parents and brother in the camp. But after a few months, the sisters decided they must escape.

Late one night they tied sticks to their backs, which in the darkness made their silhouettes resemble soldiers with guns, and snuck out of the camp. Soon after, they ran into two partisans who had snuck out of the forest looking for a doctor to care for partisans who had become ill. The sisters recognized the pair from their hometown and begged the partisans to let them join them in the forest.

“I said, ‘I’m going to follow you, even though I know you didn’t come looking for me. But if you want to get rid of me, you have to kill me, because I’m not going to let go of you,’ ” Sara Rosnow said.

So they went into the forest. Days later, when partisans returned to Dvorets in the middle of the night to bring more Jews into the forest, among those brought back were Sara and Mira’s parents and brother.

Soon after arriving in the woods, Mira met Norman Shelub “a brave and handsome partisan” — who led his own unit. “We noticed each other right away.”

The pair fell in love and married in the forest. She went with his unit, carrying his ammunition and helping the other women with the cooking and laundry. The couple promised each other that if they both survived, they would be with each other forever.

“The forest was romance, a love story, so it wasn’t exactly bad,” Shelub said. “We had difficulties, we had obstacles, but we always tried to overcome. These were not easy times, because everything was so uncertain.”

Sara experienced her own miracle of sorts. A tenacious teenager, she wanted to fight along with the men. A group of partisans planned to blow up a chunk of the railroad tracks, and Sara begged to be included in the mission.

The commander nixed the idea at first, convinced that because the petite, pretty girl didn’t look like a warrior, she would ruin the mission.

But she begged to go. The commander eventually relented “to get me off his back,” she recalled.

“We got a piece of dynamite, matches and a rifle, which I didn’t know how to use anyway.”

It rained all night. The ditch near the train tracks was filled with water. Everyone else was able to light their dynamite sticks, but Sara was so drenched that her matches wouldn’t light. Her comrades told her to forget it, that if she stayed near the tracks any longer she’d be blown up.

“Just as two partisans ran back to me and came close to dragging me away, the match lit. This is one miracle,” she said.

She “became a hero overnight. When I came back, the commander sent someone to me and asked me to become [the commander’s] mistress. I thanked him for the privilege, and told him if we both survive the war, then we can talk about it.”

The commander didn’t like her answer. He demanded she leave the group of fighters.

“That was the first and only time I cried for three days, because I couldn’t see a way out,” she said.

She found herself in the forest with those unfit to fight, a group that included her parents and brother, who was quite sick. The group worried that she would be more dead weight. To prove her strength, she lugged a sack of potatoes four miles.

“It wasn’t an American sack of potatoes, it was a Russian sack of potatoes. I had to shlep it, to pull it, and it was so heavy. I cried so hard because it was so painfully heavy,” Sara Rosnow said. “And finally my back was hurting me so much, and I twisted it and heard something crack. I didn’t know it at the time, but my bronchial lining had snapped.”

She became very ill and eventually was unable to walk, stand or even cough. Breathing became painful.

“I was laying on the ground and I heard my own eulogy. ‘Oh, such a nice girl — she’s going to have to go, too.’

“But after four days of laying on the ground in the forest, I sneezed. And I called to the group from the fire, ‘I sneezed, so I am going to survive’ … And that was my second miracle.”

Partisans survived the harsh winters by digging holes and sleeping in underground huts (known as zemlyankas) or hiding out in peasants’ homes. “The good ones would supply us with food,” Shelub added.

But winter in the forest could be painful.

“I had frozen hands and frozen feet,” Rosnow said. “You ate when someone could get food. It could be for days.”

The siblings tried to take care of their parents, who found life in the forest to be extremely difficult. Eventually, their mother was killed by the Germans, and shortly thereafter, their father became sick with pneumonia and died.

Mira, Sara and Morris spent two winters in the forest until the Russian army liberated them in 1944. At that time, Sara and Morris did not know if Mira was alive, or if she was, where to find her.

Mira and Norman went first to Czechoslovakia, then to a displaced persons camp in Austria. Since Mira had studied English in school before the war, she found a job helping Jewish survivors immigrate to the United States.

Meanwhile, Morris and Sara went to Germany. Through word of mouth, Mira learned her siblings were alive.

“When I found out they were in Germany, I sent them cans of apples and plums and encouraged them to come to Bad Gastein, Austria,” Mira said. They did, in 1946.

As Norman had relatives in San Francisco, he and Mira moved to the United States in 1949, settling in the Sunset District.

They begged Sara and Morris to come as well. Though the brother and sister had intended to go to Israel, they decided to follow their sister’s advice, coming to the United States in 1950.

Mira and Norman opened Norm’s Sandwich Shop near the Embarcadero, and had three children together.

In 1977, “I suffered the greatest tragedy,” she said, when Norman died during heart surgery. “I could not see how I could go on without my beloved husband.”

With the help of her children, she went back to school and in 1985 graduated from San Francisco State University with a degree in history. In 1994, at the age of 71, she earned a graduate degree in counseling, and today still works with Russian émigrés for Jewish Family and Children’s Services.

Sara Rosnow also worked as a counselor for many years. She earned a degree from U.C. Berkeley in 1956, and a graduate degree in counseling from SFSU in 1975. She met her husband, Joe Star, in the Bay Area. They had two children together, and though they divorced in the ’70s, they are still best friends and neighbors at Rossmoor.

Looking back on their partisan days, “I never lost hope,” Shelub said. “I always felt we’d succeed, that we’d get out of the forest and lead a normal life.”

After the Dec. 3 film screening, director Zwick and screenwriter Clayton Frohman answered audience questions about the film, and explained why they made the movie.

“It’s the eleventh hour now for those who were there, and their story deserved to be told in their lifetime,” Zwick said.

Though the film’s primary focus is the partisans’ will and ingenuity in the face of adversity, Zwick and Frohman deliberately inserted humanity into the film through funny and romantic scenes.

“The partisans’ stories are about more than vengeance,” Zwick said. “Their affirmation of life was their greatest defiance.”