Early waking-ASD

My son (6) is being assessed for ND. He has always been an early waker but it’s currently now at 4.30 am…he gets up , shouts, wakes everyone up and I spend the next 2.5 hours up n down trying to damage limitation so he doesn’t wake my other son up. Any suggestions welcome on how to get him to sleep later , it’s making school and home life awful…I can’t cope, I’m one step from a breakdown and everyone spends there whole time shouting from pure exhaustion . I’ve tried bribes, rewards, being nice, being firm..I am lost