I don't know much about Brazil, but take this from an American perspective: since you're both adults, you don't really have to give a shit about what the mom thinks about you. I've never met a mother who didn't want their daughter married to a rich man and not want grandkids and react so negatively, so she may have personal past issues with men not relating to you. You never mentioned the dad, so I'm assuming he's gone, and that may have something to do with the moms hostilities. I don't see any issues with the rest of your girlfriends family and her friends besides the mother.

You can also have a straight-up-serious talk, one-on-one, with the mom about your intentions to be with her daughter. Try to be as polite and gentlemen as you can be with her. It's important to keep your cool regardless of how she reacts. If she still acts inappropriately hostile, disregard her opinion for now and shame her through kindness. That'll either let you grow on her, or really piss her off. Also known as a win-win in America.

I'm going off of your post, and from what I can tell, this misery you describe with your girlfriend can be remedied by referring to my first sentence. I would recommend not to break up with your girlfriend if you're serious and thinking about marriage. If you do get her pregnant, stay with her. I think that's pretty self explanatory as a man.

Friends come and go. Most good friends are usually coworkers, or at least people you see on a daily basis. I wouldn't recommend cutting off ties and burning bridges needlessly since you don't have to. Personally, I would only do that if someone was taking advantage of me financially. There's always time to make new friends, especially as you grow older, work, and establish a career. You'll still be making friends in your mid twenties, thirties, forties... etc.

I can't give you sage life advice since I'm the same age as you. What I can give you is peer advice. Don't pass up a good thing (your girlfriend) because you think you're miserable now. You may regret it much later in life when you see your hypothetical-decided-to-breakup-with-then-girlfriend post on her Facebook that she got married to some other dude that isn't you four years down the line. Then you'll really feel miserable. Now that's when you can post your next bullshit rant. I won't be as nice next time. I was searching for laptops when your post came up first. As an American: Fuck. You.

tl;dr Don't give up that pussy so easily.