I am WORRIED about you. Here I would tell you to call 911 (police emergency number) and have them send someone EVERY TIME that he gets physical. Hitting your husband, esp in the privates, is ASSAULT and DOMESTIC VIOLENCE and husband can press charges against difficult child which would mean he is ARRESTED. In my area they will come and talk to a kid a few times before taking them anywhere unless you insist and won't give in when they try to tell you they "can't". I had to do this when Wiz was 14 because he knew he was bigger and stronger than I was and one of us was going to end up in the hospital or morgue and the other in prison because he was determined to beat his way through me to go attack Jessie. Just wasn't happening and to protect him I insisted he couldn't live iwth us. It was hugely traumatic and NOT medication related. We had done all the medication tweaking possible and he is on the same medications NOW as then and is a totally different person - a delightful one1
Anyway, I suggest if at ALL possible you call the police when difficult child is at school and ask what your options are. You also need to have both you and husband go to the therapist and learn how to do a therapeutic restraint and get the documentation that you have been trained in this.
A panic button is a good thing. Here you can get them for about $25 a month on the low end of services and this might be enough but I don't know what is available in your country.
I know how hard it is to even THINK about calling the police on your child, but something has to happen for him to start using his skills and tools because if he hurts people he is going to end up in some type of jail, even if it is one for kids. I know in our country that we seem to have a lot more kids getting mad and killing people and we must work to stop it. I think part of that MUST be parents having no tolerance for a violent child. I lived iwth one and did the restraints and have a LOT of physical problems that were made much worse after dealing with all the physical altercations with my child. I really really wish we had not just worked with therapy and medications but had brought the cops in earlier to show him how unacceptable it was. He thought it was funny to see me hurting the next day from where he hit me. He also felt very powerful and satisfied. Now he HATES that hte had those attitudes and sees how wrong it was but getting to that point took years and our relationship won't really ever recover.
You also MUST make your younger child a priority. We learned that when we were not looking or when we were asleep at night that our son was TORTURING Jess. She would be sound asleep and he would go and hurt her badly and threaten to kill us if she told. Sadly we learned that this is NOT uncommon. You MUST make sure that your youngest is NEVER alone in a room with your oldest, not even long enough for you to go potty. Make the youngest come with you and stand in the shower with the curtain pulled so that privacy is respected and everyone is safe. IT sounds extreme and is, but if your son thinks NOTHING of hurting your husband, I am darn sure that he is hurting your other child.
One thing that really helped us sort of "reset" Wiz was getting ALL the violence out of the house. NO violent tv. Not even DISNEY because those shows have a LOT of violence. We went to the kinder, gentler shows - Winnie the Pooh, Barney, Blues Clues, and yes, Wiz HATED it but he had no choice because if putting it up in our bedroom didn't work we gave them away or got a storage unit miles away to keep them in until he was able to handle them. We cancelled the tv cable service and only had the few channels we could get with-o that, and we locked up the tv if Wiz got up and watched it at night with-o permission. We locked down the computers and we censored his reading material. We limited what he could check out at the school library and we did not give permission for him to watch ANY video or have computer priveleges at school. WHen school ignored us and did a lot of other things that were problems, we pulled him out and homeschooled him. We felt it was our job first to teach him to be a good person and second to educate him. The first year we homeschooled we did little other than go to appts at docs, psychiatrists, tdocs, etc.... We had a LOT to undo. At his age he wouldn't even THINK of asking for a horror dvd because he KNEW that not only would he not get it, I would probably laugh hysterically at the mere thought. If we couldn't let him watch Beauty and the Beast or Lion King, NO WAy was he watching horror movies.
The media they watch has a HUGE impact on how they think and what they think is OK to do. I firmly believe that we are seeing more violent kids because the kids are seeing so much tv and computer and video game violence. I believed this before I had kids, I fought and still fight to limit my children to age appropriate things - not age in years but age in emotional maturity and what they can handle. My younger two have never been violent except when severely provoked and they get to watch a LOT that Wiz never did. I firmly believe that most video games are too violent for most kids under 10. I HATE what I see a lot of kids playing when I go past computers at the school and at the library and at area internet cafes, etc.... I don't think it is good for them and for the difficult children it is teaching them that it is okay to hurt people. That is NOT something that will help them in life and will not help anyone they are around.
That is my thing. I would limit what your son is EVER allowed to see for the forseeable future. Not just no horror dvds, but no dvds that are adult in any way. You and husband can watch tv after he is in bed or figure something else out. What you can't do is continue to allow him to hurt you. Calling 911 is what I would advise here. I would probably ask for transport to a psychiatric hospital for a mentally unstable, violent child rather than hiding in the pantry. I would go into the pantry with your youngest to make the call, so that difficult child cannot hurt you, but I wouldn't go in there and hide until he calmed down with-o making that call.
I hope you have those services available. I know you probably don't normally let him see horror dvds, etc... but if you watch news shows and even kids shows with an eye to if there is violence in them of ANY kind, I think you will be shocked at how much is there. For our family I had to remove ALL of it and it DID help. Even now Wiz says that while he HATED it he did NEED us to do it anyway.
I hope something I have said helps.