I found this scene from Step Brothers of the two brothers sleepwalking. They are seen with their arms slightly outward when they walk into their parents' room. I consider this an inaccurate portrayal of sleepwalking because sleepwalkers actually do not walk with their arms out or in a zombie fashion. True sleepwalkers walk as they would when they are actually awake, with very few differences. The step brothers from the clip also are mumbling to themselves and seem to be interacting with each other. It would not make sense to me that someone would be doing the same act as someone else while they're asleep. In other words, how are they asleep yet communicating that they need to bring the presents and the Christmas tree into their parents' room? How are they both doing the same thing? This is another aspect of the scene that is unrealistic/inaccurate. The mumbling, however, is not unrealistic. Web MD says "In some cases, sleepwalking is associated with incoherent talking." They also say, "on questioning, responses are slow or absent."
One of the most important parts of this scene to analyze is when the dad wakes the sleepwalkers up. Before he does this, the mom says "Never wake up a sleepwalker." And upon awakening, the men start screaming and flailing their arms. So, the movie is portraying that sleepwalkers get angry upon being woken up. The attached article from the New York Times claims that it is not dangerous to wake a sleepwalker, but they may be confused.
Overall, this scene from Step Brothers was not an accurate portrayal of sleepwalking, but if the writers had made it accurate, it probably would not have had entertainment value.
Web MD: http://www.webmd.com/sleep-disorders/guide/sleepwalking-causes