his behaviour is like any normal child but is also on a tight ship with Emmett. He's known to obey his elders' commands or face the consequences. Seeming fairly normal, Jack may be putting up a facade to hide his true feelings and thoughts. Extreme trauma, fighting, and Emmett’s disappearance most likely lead to the downfall of his mental state. His journal entries also mention having trouble sleeping, which is probably something between the paranoia to PTSD spectrum due to the fire. 