I agree with others - sounds like more going on that just ADHD and ODD. I am not sure what state you are in, but here in NY we have something called Mobile Crisis. If my difficult child is acting violently, brandishing a weapon, or threatening one of us we can call the number and the police are dispatched for safety ASAP and then a team of 2-3 social workers, psychologists and or psychiatrists come to wherever we are to evaluate the risk. Outcomes if they cannot establish safety include the difficult child being removed by ambulance to a psychiatric ward for evaluation. As I only have the difficult child at home and we are his targets I cannot even begin to imagine how or what I would do if I had to protect other children from him. He is also big - 6'1" and 200 lbs at this point at 17 YO.
If you do not have an equivalent to Mobile Crisis in your area, I am sure there is some service that the state or county offers that you should be able to tap. At a minimum in my humble opinion, safety is the most important factor and if difficult child is threatening his siblings I would probably call the police.
I think, especially with a pattern of documented incidents it would be easier to establish the need for removal from your home at least temporarily for his and other kids saftey to a residential treatment facility. In my area we also have residential schools for kids with violent tendencies with and without mental diagnosis. In NYS they can, if eligible, stay until they are 21.
Good luck - I will be thinking about you. I just found this forum a few weeks ago and it is so helpful to know that I am not alone in this constant struggle.
