It sounds like you are headed the right direction with residential services. Unfortunately, from what you describe, at the present time he is truly unable to function safely in a home environment. I suspect residential placement will be the best choice for him as well as for your family and pets.
The child who brought me to this forum is my Difficult Stepson, who at 15 strangled my wife (his bio mom). He is 6'5" and over 250 pounds. Though I did not enter his life until he was thirteen, my understanding is that he was always troubled. He did grow to become big, strong and dangerous.
At least for now, the only advice I would offer is sadly, place him outside of your home where he can be safe and hopefully receive treatment that will allow him to return one day.
