In the film, Edmond killed Issac
In exchange for his life, Edmond was recruited to help kill the younger kids. They had their heads covered so he didn't know for sure his brother was among them until after the fact. This is what he is dealing with more than his wounds. The war is over super powers
This brings Edmond's powers into the framing war. The guerrillas were either fighting to suppress or bring freedom to those with psychic powers (this can freely go either way). Edmond was being kept at the farm away from society because of his powers - this can work no matter the reason for the war - to keep him out of the main battle or to keep his powers secret from society. Leah helped cause/worsen Daisy's eating disorder
Early in the book, it's mentioned that Leah told Daisy that Davina was 'trying to poison her.'