Well, I haven't had this issue with my boyfriend or his family, we don't live together yet and we tend to get along pretty well with each other and each other's families. However, we have had an issue about his mom and money and the way she handles their household money (it's just the two of them and she's been leasing their home for like 36 years...coulda paid it off by now right?) and she meddles into his financial affairs and makes comments about how 'broke" he is in front of me. For the record, he's not broke, he just doesn't tell her how much money he's got and he makes a point of being very thrifty. It's embarrassing to him and makes me uncomfortable when I'm around and she says things like "Your bank called today...what did you do, go over on your card again?" then turn to me and go "If you guys live together, you better keep some money away or he's going to have to guys living in a shack." In fact, he has more money than I do, better credit than I do, and is just generally smarter with his cash than I am. Also, he gives her a few hundred dollars a month to help out with bills and things. Well, the bills probably wouldn't be so high if she didn't leave the TV and Lights on for the dog during the day and run the AC with the windows and doors wide open. They'd probably be a lot lower if she hadn't just bought all new furniture for the bedroom that she refuses to sleep in. And maybe if she canceled the premium cable in that bedroom...gasp...even lower.
As much as that bugs the shit out of me and as much as it's hindering his savings for moving out, I can't do or say anything about that and need to tread lightly when I express my opinions about the situation because that's HIS mother, HIS money and ultimately I have no say.
Your situation is slightly different because you guys do live together and share bills, so whats yours is his and vice versa. I don't think it was right for him to blow up an argument about his family or expect him to take your side against family. It's his family, you can't ask him to keep them from coming over. My suggestion is next time something like that happens, perhaps leave for a while so that you don't have to be bothered by it and he can spend time with them arguing and watching TV and whatever else without completely inconveniencing you. Perhaps find a way to to gently and calmly explain how you feel and how disrespected you feel that he doesn't make a better attempt to put his family in check, but if that still doesn't work, you may just have to grin and bear it. One of the replies above hit it right on the head, when you marry the man, you marry the family. Also, maybe having the conversation right after he's just argued with them and put them out isn't the best time.
1. Put a password on your computer; if you don't want them on it, don't let them on it. You have that right because it's your property and you pay for it. You're not a library, if they wanna get online and download music or watch YouTube they can do it at home or elsewhere.
2. As far as your TV goes, they have one, why do they need to watch yours? Maybe--as politely as you possibly can--let them know that its your house and your tv and you'd like to watch your shows alone in your home. If you're calm about this and they fly off the handle, don't shout back, they're in the wrong if they start getting pissy, as you're simply trying to protect your rights to your time, space, and property.
3. Suggest that your boyfriend go to their house from time to time to visit, and let him know that he needs to put his foot down and tell his family to have more respect for you and you guys' place, you shouldn't be put out because his family is rude. But you can't expect to be rude to his family or to him regarding his family, because they were his family long before you were his girlfriend.