I'm just going to chime in with everyone else here and say that you should definitely move. It is NOT taking the easy way out. You've struggled to make this decision-there hasn't been anything easy about it. You've got to do what is best for your boys and your relationship with your FH because that is going to be strained eventually because of this.
You certainly don't owe them anything. If your first husband had wanted them to have some of that money he would have stated it somewhere. What is happening here is that they are sponging off of you and since you have been doing it for so long they now feel a sense of entitlement. Sounds wacky, but that's what's going on. When you told them no it made them angry and since they are so used to you giving in, they made threats-empty ones of course-but still threats. They believe that you will back down and that is exactly why you cannot. This will just continue if you do.
I totally agree with the poster who said that not everyone on disability is a deadbeat. I've known some people who have been on it and are truly deserving of it. But there are people out there who will abuse it just to get 'something for nothing'. In PA it's very easy to get disability. Basically you need a doctor's word that there is something wrong with you-and there is no shortage of crooked doctors or docs that just don't pay enough attention and sign the papers to get you out of their way.