What was the name of that movie about brothers adventuring north American wildlife?

What was the name of that movie? (I think it's allegedly based on a true story):  3 brothers (2 adolescents and the youngest is under 10 I think. or were they4 brothers?) leave home for an adventure in the wild nature of north America. The climax of the movie is when they enter (and escape) a cave of bears. Before going in the cave, they meet the wife of a man who, if i recall correctly, was killed by the bears. The wife tells them not to go there.

The movie has many wild nature scenes, and, if I still remember, some original shootings that were taken by the real brothers.

OK - that's about all I can remember. Any clue you have will help. thanks!