I guess I need a bit more background info.
I'm a special education teacher, and I've worked with a lot of different kids, with a lot of different issues. Most of the children I teach now are within the severe/profound range of disability, but I've worked with high functioning students and students who just needed some extra help with everyday living. This does NOT make me qualified to place any type of label on your child, but I do happen to know a few things about 12 year-olds. Hey, I have a 12 year-old boy of my own! And an 11 year-old son!
How are his grades? Are they sliding downhill? What does he like to do in his free time? Is he eating and sleeping well? I guess I'd like to know a bit more about what he's specifically doing to drive you nuts...I know he argues with you, picks on sister, etc. Here's my advice...never argue with a 12 year-old. Once it begins to lead into an argument, you end it, there and now. Say, "We are not going to do this. This is DONE." And then you send him to his room, and walk away. As far as picking on your daughter, how normal is this? Siblings fight. Siblings can be downright AWFUL with each other. Solution...separate them immediately. If they cannot be nice to each other, then they can sit on the couch holding hands for a half hour. I'm dead serious about that! That will make him think twice about picking on her again...who wants to hold hands with their little sister on the couch for a half hour?
I'm sorry to hear that your son has had a lack of strong male role models in his life. This can be hard on many a boy. However, 12 year-olds are a special breed. They're caught between "kid" and "teenager." They become headstrong, sometimes disrespectful, and they WILL test your boundaries, and see how far they can push. You cannot relent, you need to draw the line, and he needs to know where the line is. If he crosses the line, you administer the consequence (which he should be aware of before he crosses).
I guess what I'm saying, is that it is wonderful to have empathy for children, when they've been through rough times and situations. It's fine to allow them a certain degree of anger, and it's fine to maintain a dialogue about your son's feelings. But we also must not allow our children to behave like victims...they are accountable for their own behavior, and in the real world, others will NOT cop deuces for you if you didn't have a strong male role model in your life as a child...unfortunately, this is life.
I don't want you to think that I don't feel bad for the problems your son has had. But, there are things that cannot be allowed, such as arguing with one's mother, or picking on little sis...and being angry about certain aspects of one's life does not excuse the behavior!
12 year-olds are tough, no doubt. My own drives me crazy sometimes...and I know that this will continue until around the age of...well...35, probably.
Here's a squeeze for you...hang in there! Being a parent is a tough job!