Chief Saint Cloud is running a summer camp that teaches practices of his tribe to young men, including their mythology. It's a way of keeping his tribe alive.
Chief Saint Cloud is well aware he's sending children to fight against impossible odds. However, they're people he's been teaching his ways as part of a Summer Camp so those ways won't die out. They're also fighting against white men here to steal his people's land. No wonder he's taking this completely seriously.
Ernst's dedication to stopping the assault on the camp is certainly helped by his guilt over being tricked. He's The Atoner for his foolishness in trusting Krader.
Why can't Moose swim? Given his age, and depending on how long he's been in the detention center, he was likely sent at a young age, before he would have been given swimming lessons.
Krader managed to get that family from the beginning off its land, so they're still screwed.
Though given the events of the film, Krader's business dealings will likely be subjected to legal review. They may not get their land back, but a hefty cash settlement could be in their future.
