normal family who have done their best, and ended up with one (female) child who had turned out lovely, which highlights that they were not the cause of the boy’s behaviour.
I think this is the most important bit of it all. They are a normal family, obviously not to blame... And yet...
Dad is the decision maker, the head of the house.
Dad was physically abused by his dad
Dad's temper is barely held in check
Mum and daughter manage dad's emotions, help him to regulate
Dad is ashamed of son not being masculine
Dad can't find a way to connect with son so allows him to spend hours alone
Son allowed to wander streets at 13 until around 10pm
Mum seems entirely absent in parenting son. She's home in the evening, but imposed no reasonable curfew or encouraged him to get out of his room. She allowed dad to take son to football and boxing when those activities wouldn't suit him. Son's opinion of mum is that she makes a good roast dinner.
Very traditional gender roles in the family. Subtle "harmless" misogyny eg dad calling mum and daughter "girls". Mum asking daughter "is your boyfriend looking after you?"
Jamie doesn't fit this family's image of a son. Jamie is small, slight, weak in appearance. His interests are typically "feminine". He feels inadequate. By his family's expectations of gender roles, he is inadequate. At the same time he's given the implicit message from the family that men should be pandered to, listened to, appeased. Then he's allowed free rein on the internet. He is the perfect target to be radicalised by incel narratives. Entitled, inadequately 'masculine' , not meeting his own expectations and very vulnerable.
And then he meets a girl who doesn't treat him like his mum and his sister treat his dad.