It sounds like his father's treatment of you is a tremendous influence. If you are now separated or divorced, your son is transitioning between 2 households where the discipline style is not the same. He may be hearing things about you, about how men have to boss around the women in their life, and so on. I would have suggested taking away all the electronics which kids think are essential, but you say you have done that. And if father pays for them and gives them to him when you're not around, that's a problem. But you can still control things in your own house unless you are afraid that he will want to live with his father and you can't live with that. But I think you have to take that risk because otherwise you will have another 3 years of hell, have your younger son see this and grow up the same way, and no matter what, you will have an older son who is just like his father.
The loss of your younger son is wearing on all of you. Your teen may have underlying fears, or he may be an opportunist who realizes that losing a child is so painful for you that you will give in to him rather than lose him to his father. Perhaps he feels you are responsible for the loss of the brother - kids often have limited understanding despite their age - and be trying to punish you in some way. That's a job for a therapist.
I would also remember he's going to expect to be driving in a year or so - that is powerful motivation. My brother was disrespectful and defiant, and that's what my parents did. They let him get his permit but then withheld the car, which was more immediate. Disrespect today, no car today. Disrespect the next day, no car today and tomorrow. My neighbors did the same with their daughter. She kept mouthing off, and they grounded her for a week, then two. She kept yelling and they said, "Okay, a month." She screamed, "Oh, why not TWO MONTHS?" They said, "OKAY!" After about a month, she really changed her tune. It was HER CHOICE to stay grounded because she kept up with the attitude.
Your son probably doesn't want to hear any lectures that skills don't miraculously appear when he gets his own place. He's also not going to get his own place until he has a really good paying job, which he won't get or won't keep if he is lazy, has no work ethic, and treats people like he's the boss. You can let him know that, if he wants a girlfriend, he needs to learn to listen more, boss less, and have a work ethic. If he doesn't want a girlfriend, he's on the right track!
I think that you can try to do this now, or you can just ignore him and walk away. I'm not sure what you mean when you say grounding hasn't worked and taking away privileges doesn't work. Why doesn't it work? Because he sulks and rants and still treats you in a nasty way? Okay, so then what happens? Do you give in and restore the privileges because it's too exhausting to hold out? Does he wear you down and you feel that the punishment is not effective, so you give in? You've got to find a backbone and just outlast him. You have survived so much, so you are much stronger than you give yourself credit for. You have perspective, you have the long view and are not just dealing with today, you are dealing with his future. He is a teen, his brain is not fully developed (especially the part that predicts risks and consequences), and he is living for today.
There was a book that was popular a few years ago - something like "I hate you. Will you take me to the mall?" - about kids who are horrible and then want a favor or a privilege. A teacher colleague used to recommend it to all the middle school parents we were meeting with in conferences who were all talking about kids who didn't do their work or gave attitude. Your library probably has it so don't spend the money, but it might give you help and support.
It's been said that children's job is to go to school and grow up responsibly, and to have the best possible time doing it. They have a lot of control and make a lot of choices, but they have to own the consequences of NOT doing it. Losing privileges and staying home and not getting a ride and not having dinner cooked for them are THEIR CHOICES, based on their actions. I would let your son keep his own room the way he wants to - and just close the door. Public spaces are another thing. Those you may hae to clean up, but that means taking all of their stuff lying on the floor and putting it in a big bin or a trash can. They want it, they look for it and clean it off. That means backpacks, shoes, jackets, wallets, iPods, ANYTHING. Don't sort, don't match shoes, don't keep track. IF they are old enough to defy you, they are old enough to keep track of their own junk.
I would put him in charge of his own stuff, his own lunch, his own laundry, starting today. Teach both boys how to do laundry and fold sheets and that sort of thing. If they won't listen, that's their problem. DO NOT pick up their clothes, put them in the hamper or the wash, do not fold or put away. If they leave stuff lying around, oh well, they won't have anything to wear. Nothing horrible will happen if they wear something twice, wear something wrinkled, or wear something mismatched. They will scream but so what? They'll probably say that everyone will know you're a bad mother, to which you respond that, if they want to tell their friends that they themselves are too stubborn or too incompetent to pick up their own things, that's up to them. You don't answer to their friends or to public opinion.
If they don't want to go to school because of it, if you can't force them on to the bus, let them stay home and do the laundry, and then on the way in to school, they sign in at the office and sit with the principal to explain why it wasn't important to them to do what was expected. You do not write a note, tell a lie, or bail them out.
I do think you can have higher standards for the 15 year old than the younger son, but I think it's essential that the younger one have some responsibilities and that he begins to learn some skills. Laundry is where I would start. It's what worked for us. Sweaty boys and sports stuff.
There are no rides to activities. There are no lunches made. There are no demands about dinner. If you feel you must cook, then do so and leave it on the stove for them to serve themselves. Do not make breakfast or lunches - they can get their own breakfast and make their own lunches, either at the time or the night before, depending on their summer activities. If you need to take them to a summer camp for the day because you have to go to work, fine. But nothing else. No rides to friends, no parties, no weekend activities, no luxuries. If the little one behaves, he gets a ride. If the older one yells and finally says, "Okay FINE! I picked up my backpack, are you satisfied? So now drive me," the answer is no. Keep up good work and no mouth, and I will drive you tomorrow. Keep up the mouth, and no ride tomorrow. Do not let them blackmail you and say "Okay, I'll walk and if I get kidnapped, it's on you." That's emotional blackmail and you can't give in.
I'm telling you now that this is going to get worse before it gets better, but you CAN do it. The more he acts out, the calmer you have to be. You DO have the control. If your ex gets in your face about it, you don't have to listen or be berated. You have to talk about their health and their education and safety, but not about laundry or cell phones.
Good luck with this. I know it's hard. But they DO come around. If you don't do this, you will have 3 years of hell before he graduates, and you will have added another abusive man to the dating pool.