Yikes. DA might be harder to nail than PD. At least the PD is on your side.
Pardon the rambling for a moment, but maybe this story can give you an insight into some steps you can possibly run through on your end over there. I once had to take on a case worker from a government agency. This was during the period in my life where I had no choice but to accept food stamps and medicaid. I was pregnant with my first child, and had to move back in with my parents. The state had promised my child medical coverage for the first year of her life. Six months roll by and I received an envelope with tons of paperwork and forms that they requested I fill out. I called my case worker and asked her to please call me back, as I needed help filling it all in. She didn't call, and didn't call. A week or two passed and the deadline was coming up. I called and left her another voice mail (she didn't answer her phone) and asked that she please call me back, as I would miss the deadline for the paperwork if she didn't return my call. Not 5 minutes later she called back and actually started chewing me out on the phone. The conversation from her started off like this: "Well it's YOUR FAULT." She told me the deadline for the paperwork was the following day early in the AM. I was shocked and didn't know what to say so I told her I would do the best I could on my own and turn it a little later in the day (1 day early). I did so. A week later I got my paperwork back in the mail and she attached a letter saying I had missed the deadline. She switched it to just after the phone call so that my paperwork was going to be revoked due to lateness no matter what. I was livid. They yanked her health insurance. So I decided to write a Michigan Senator. In my letter I explained what went on in great detail, and attached a really good photo of my daughter to it. The impact line was something along the lines of, "This is the child whose health insurance is being denied due to the vindictiveness of my case worker." The Senator took swift action. In the end, I received several apologies, including one from the manager of the head office in Lansing, got her benefits reinstated and was assigned a new case worker. In fact, her entire office was even shut down for a week to go under evaluation to see if anyone else was being mistreated as we were. The only tidbit of information I didn't find out was whether or not she got to keep her job. All I wanted was what was promised though, and we got it, so I was satisfied.
In your case, I would find some of the best pictures of your kids, and your family as a whole. Make sure your eyes are visible, and hopefully bright and shining. Pictures speak a thousand words. Present these pictures to the DA (and the news), and let them know that the news stations have copies of these to run with the story of your murder. That is, unless, the DA decides to take action against the man who has been repeatedly threatening your family. In fact, I would be charging him with three counts of attempted murder based solely upon the incident involving your two sons and your husband. And then if we step back and review the previous incidents, the fact that he was walking around your house looking in the windows with a flash light should have at least warranted a charge of trespassing with intent to break and enter. You don't just stalk around someone's house at night with a flashlight looking in the windows unless you've got intent to enter. The DA there sounds lazy. They are supposed to be serving the public, which they are obviously not doing.
As a precaution, you guys need to start carrying cameras on you at all times so that you can photograph the nut when he's near you. If you've got a video mode on the camera, all the better. You can catch him ranting and saying things to you. The more evidence you have to show the court, the less room the DA will have to let things like this slide. It's unfortunate that they are making it this hard for you though.
Good luck, and I am so sorry you have to go through this.
ETA: You might want to consider finding a really good Pro Bono lawyer.