I think they're doing a hamhanded job with Chris (well, with everybody) but I think what they're going for is that he's having a PTSD response to the situation and he's a terrible communicator because he's 15, but he's not psycho.
His dad kills his mom. He kills the zombies at the fence. He does the mercy killing in the plane. He regrets not shooting the pirates before they boarded and feels intensely guilty about that, and then the pirate dude bullies Chris into killing him too, and Chris thinks for about 30 seconds that he's done the right thing and then it gets worse for him.
I can totally buy him freezing when Madison's being attacked, he's been grinding his gears for a while. And I can totally buy him being frustrated while trying to communicate with Alicia but she doesn't want to hear it. And then she's biased when she goes to Madison about the threat. So Madison is super biased when she goes to Travis.
He went to the bedroom wanting to talk it out with Alicia, she didn't wake up and he gets distracted by the shiny knife that Madison isn't supposed to have.
He's not crazy, it's all circumstantial and will blow up and be resolved in a family moment of understanding, probably mediated by Nick and Ofelia.