How frustrating for you, both to be in the situation and then to try and get help and be put on a waiting list.
Without knowing specifics about how he behaves other than the emotions you see him display it's kind of hard to comment specifically. But I do know that you are right, you shouldn't have to walk on eggshells.
One thing that stuck out to me was that you said you have been dealing with his behavior for about for years and coincidentally you also have a 4 year old son.
The other thing that stuck out (and this may have just been the way you wrote your post, not necessarily how you actually talk to him) was that you said a couple times that you "ask him what's wrong" and he doesn't open up and your husband "talks to him and tells him he needs to make right choices".
My suggestion would be that you do less talking and more listening and see where it gets you. But, with kids, the key is that you can't do it in an intense setting, the "sit down and talk" method isn't generally going to work. So, as you are setting the table use empathy and see if you can get him to expand. For example, "You were really upset earlier when you were playing the game. That was frustrating wasn't it? I know I get upset sometimes when things don't go my way"
You may be surprised at what his response is, if he thinks you understand what he's going through.
The being angry at his brother thing is a hot button. He may be resentful and feel like he has lost you because of his brothers needs. He may talk softly because he "literally" doesn't think anyone listens to anything he says.
Try and see if from HIS perspective. Not the perspective you think he has or you want him to have or you would have if you were him.
I also think at 7 he should have some activites that are JUST HIS. Is he in tae kwon doe? Does he swim? Play soccer? Get him into an active sport where he can use some of his energy. It's also just for him, so he can feel special.
Also, write down specifics about what he does and what his triggers are - that will be helpful when you get into counseling.
*One additional note - if he's never been to a babysitter, does that mean you and your husband have never been on a date without the kids? You MUST fix that immediately!!!!!!!! Once a month - AT LEAST - find someone you trust, leave the kids and go spend time devoted to being husband and wife!!!!!!
Good luck!