Ya, you really are between a rock and a hard place. It sounds like you are the only one who tries to change his behavior and also the only one who makes him do his homework. Combine this with the fact that he MAY have ADHD, which just makes everything that much tougher for you (and him).
My first suggestion is to find out a little bit more about ADHD and how it affects kids. If he does have ADHD, it does change how to work with him and also explains a lot of his actions. This is a pretty good link with info on the symptoms of ADHD - http://helpguide.org/mental/adhd_add_signs_symptoms.htm
And if you do feel like he has it, then I would also suggest that you buy the book, "The ADD/ ADHD Answer book," by Susan Ashley. Its only about 10 bucks on Amazon and it will give you lots of ways to work with him. Also this is a good site with ideas on ways to do homework for kids with ADHD and actually they are good ideas period. There is also lots of other good ideas on this site - http://www.additudemag.com/search/keyword/Homework%20and%20Test%20Help.html
Now he may not have ADHD. Its possible that a lot of his actions are due to the lifesyle he has been forced into and this is his way to cope. But, many of his symptoms I have seen before over on the ADHD forum where I am also the CL. And I can tell you that no matter what he has, if you can understand where he is coming from - it will change your feelings about him. And yes, I would definitely try and get a professional evaluation or have the school district do that. I'm not sure if you need his moms permission for that or not. By the way, there is a very strong genetic component to ADHD and from your description of his mom, I kind of got a feeling where he may have picked it up.
Its possible he does not like coming over due to the fact that he has to do his homework. I will say that a child of his age should be spending no more then one hour on homework a night. Now if he works for 15 min. takes a break and then comes back and repeats that - its ok to spend more time. 3 hours is counterproductive. You need to back off. I completely understand why you feel its important to do it/help him. (I taught 5th grade for many years so understand the importance) But this is not working! Pick the most important and let some things slide. And, by the way, if he does have ADHD its very common to spend this long on homework. And its a waste of time. Frankly, I would go a bit more for quality of life. His grades will go down I am sure and sooner or later the school will make enough noise that someone else besides you will listen. And thats a lot of the problem here. Its just you. You need an advocate.
Behavior wise, unless your husband buys into what you are trying to do - its gonna be really hard to change the boys behavior. He is old enough that if you read a book called "Love and Logic" by Fay and Cline, you will find some great ideas that your husband might buy into. Also the ADHD book by Ashley has a good section on that.
Hope some of this helps! Good luck. Oh, if you have any questions about the ADHD thing, you can also get in touch with me here -
http://www.medhelp.org/forums/ADD---ADHD/show/175