Hi eagertolearn
It sounds to me like you have gone above and beyond for your sons, and are really dedicated to them.
I could use support in learning how to manage the outbursts of rage (directed squarely at me) and how to help my other children not provoke him -- it does feel like we are walking on eggshells on the time. Most recently he's resorted to telling me I am stupid, a f*$&ing b*$#@, I should die, etc... I have become numb to it yet try to set boundaries where i say if you call me these names, I will not respond to you.
I'm not sure I have the right answer, but I would say to do something more than not respond, I would set a clear boundary especially with physical violence and remove a privilege or resource that you provide, for a clear and expected number of days. If you decide it ahead of time you can make sure not to respond in anger, but just to enforce the already decided consequence.
its my experience that actual consequences can change behavior. If he loses access to gaming console or Internet or car rides when he does the worst current behavior, he may stop that behavior and in the process make a few small changes. I would focus only on one behavior at a time, so that you can also provide positive reinforcement the rest of the time, and are not punishing him all the time. Just the worst thing, try to eliminate it. Then after a bit move to the next worst thing.
I haven't seen it on here but I like the book Transforming the Difficult Child, it talks about the combination of consequences with positive or neutral attention. I find also that if I do give a consequence, then psychologically I'm more able to also combine that with attention, while if I do not, then I want to withdraw myself. But if I know they are upset that they lost something, I can be sympathetic emotionally while enforcing the consequence and making sure they have a concrete effect of their behavior that they do not like.
Good luck navigating through this time! I hope you will keep posting here, it can help. Would love to hear how you are doing.