Advice on my situation

This would be an angry dome thread but I'm at a loss here. Hell for once I don't even know how to start this whole thing, but here goes nothing;

 Introduction to Sin

The sin being my sister. I've made maybe half a dozen threads about her, but my god has she left me speechless this time. This is a girl, that is beyond teenage angst, beyond teenage apathy, by nature she's just an inconsiderate monster who will gobble you up and spit you out under any pretense that you disagree. You may say she doesn't fall far from the tree from me, but she's on a whole different level of idiocy. Her hypocritical view points and direct contradictions within minutes of her statements go to show this to such a degree it's not only painfully obvious, it's embarrassing.

For example, right before leaving for the beach last week, we we're getting our sh`it packed in the morning. My girlfriend and I, we're effecient, we got it done in like half an hour, maximum. My sister/mother, took nearly 3 hours, and just being plain silly about what they were packing. None the less I was able to get into my car. Well my grandmother said she'd be here at like, 12 PM, and I decided to wait until she was here. My dad said I should just start going now, my sister quick to the trigger stating "Why are you waiting for grandma, just pack up now, that's stupid". So I started at 11:40 only to get a call about 11:55 stating she's gonna be late in half an hour. Unfortunately there's perishables, and about 4 suitcases so I decided to just take out all out. My dad questioned my sister of why I was removing her luggage instead of helping me in 104 degree weather. She stated "If you guy's weren't in such a rush then you'd not having to unpack it like a dumb ass". Of course at this point I kind of flipped out stating it was her suggestion in the first place and that basic math would suggest my timing was pretty goddam precise only to be followed with, "You should have waited for her to call" with the most ludicrious eye roll ever.

To give you an even further idea, my girlfriend has been here like 2 months and absolutely finds my sister ungrateful, dispicable, and just frankly retarded. She has NEVER spoken so bad about someone, and this is based off actions taken against my family, not her. Hell my sister LOVES my girlfriend, but she can't even hold face long enough to show how little she cares about us. She wanted her curfew bumped to 3am over the summer, and I mean out and about. Eventually it reached my dad ear's where she begins to belittle him and say he's just on a power trip, instead of accepting her, in my opinion, gracious 12 am f`ucking curfew. So not only did she disobey him anyway that night, and call him essentially a power tripping community, but did so all on the same day my dad bought her $500 plane tickets to go to L/A to chase her dream of being in the music business. And the next f`ucking day my mom spent $300 on her for clothes, because apparently she needed more summer apparel, only to act obligated that she pay for them. She has a job, sure it's part time, but she makes money, as much as I did at her age, if not more. Hell it gotten so bad that when my girlfriend was having an earache because we think water got into ear. My mom gave my sister $20 bucks to get her and my cousin cheesecake slices, because they wanted it. I took them with me as my mom asked me to take a side trip for them. There was justified reasoning that I won't get into, so I did. So they talk either as I'm not there, or she once again doesn't care, where my sister goes on to say "I don't care what my mom says, i told her once I spent one paycheck here, shes buying me else for me". I kept my mouth shut, but my speed shot up from 40-60 out of anger. lol. That's what I'm dealing with. Every.Day. And if my girlfriend wasn't here, I'd consider it normal because my parents seem to not be phased by it.

[spoiler=Why god's hands are tied]

So you maybe asking "Well why DON'T your parents beat her to the very inch of her life, mentally of course, no bruises show". The problem is, my mother's relationship to my grandmother was absolute sh`it until like, her mid 20's, and was even sent to a boarding school in virginia to finish up school, it was that bad. My family doesn't have that option to send her away like that, and my mother feels like any diciplinary action that would be necessary(Iguess) would destory their relationship forever. At this point I'm kind of like what relationship, and she claims she apologizes to her at some points that I don't see. My mom hide's a lot from my dad in terms of my sister. She has a huge tattoo that she eventually said "If you don't help me get this, I'll do it down at my friends basement" So it was done, and they are going to try to hide it until she's 18ish. This is a girl trying to get into acting/modeling/commercials, whatever and she has a f`ucking tattoo up and down the side of her abdomen. I have nothing against tattoo's, I'm thinking of getting one eventually, but I don't think she can ever understand the repercussions until, they smack her upside the head.

Before you tell me "Oh well you should tell your mom to grow a spine" I have done that in the sinceriest to the coldest way possible. She simply dazes out, ignores it, thinking it's not my place, and moves on. And you know what, I wouldn't care, but there are certain things that do happen to impact me, and neither of these b`itches seem to get it. My dad doesn't have much more power considering he has to be oblivious to the whole thing. He has to take a polygraph test every year or so, and if became aware of the marijuana she brought into the house, the underage drinking, the tattoo, and all that, he would indefinitely lose his job. My sisters response to this? "Well as long as I don't flaunt it and do it secretly then I should be fine, that's why my parent's don't care". God forbid ya know, act like you consider the fact that you want to protect the person who gives you, ya know f`ucking food. My mom has also kept this all a secret from my father, where before the vacation I told him how ridiculous this was becoming.

The reason I did so was because my sister is now constantly begging me to buy her alcohol for her friends, and it was just really..disrespectful. She didn't speak me for four days just to say that. Yes, the only thing she said to me in 4 days is "buy my booz pls". My mothers response? She calls my sister to tell her I ratted her out and she better be home at 12, to forewarn my fathers wrath. What happened? Nothing, my dad wasn't planning on acting on it, he was stripped of the oppurtunity to help her and now he's just going to let her figure it out on her own. At least that's the vibe I get now. It was two weeks before he was going to Geneva, so I'm sure he knew he couldn't do anything in that time frame anyway.[/spoiler]

 The purpose

My mother and my girlfriend get along really well. And they're home all day so they both get the same experiences throughout the day. Well, my girlfriend relayed to me, in faith I wouldn't bring it up to my mother/father as she doesn't want to be put in the middle, and I completely sympathesize and will confide this until my dad's is filled in when he's back, that my sister had a request.

To give a little background, she has gotten into music, playing amateur guitar and singing lessons. So she got into "street performing" with a few friends she recently met, who have amazing musical talent, according to her. Well southperry, I went to see them, and her friends are evidently homeless and use this as income. Some actually live under boardwalks. They look like hippies, and of course the classic "Oh he was a genius, he just never applied himself." They weren't terrible, but they weren't great either. I gave them $20 in their little guitar case to show some support.

Well truth be told, they are the epitome of pothead musician. Their parents kicked them out and now they are just trying to sell music, the only car the band has is like from the 90's and the air conditioning broke. Well one of them my sister has a crush on, becuase he kind of looks like one of the "one direction" boy's, The darker one apparently, curley hair. So she's been trying to support him because she think's he's fantastic and he's going to be someone. I digress, it's her decision UNTIL she starts putting that same pressure for us to support him and his dreams.

She actually went up to my mother and asked "Can't we foster him, he wants to go to college, I mean he can just live in the basement, he has no home"./pity. And let me tell you, we got a certainly well telling practice if this was allowed since he's stayed over the last 3 days under my mother's permission. Only to find the basement, where my dad fu`cking works wreaks of pot. Then my sister stoned out of her mind eats everything in sight. The b`itch even stole my cold coke, COME ON. And go to college? To study what exactly? Liberal f`ucking arts? Guess who's going to be carpooling him. YOU'RE LOOKING AT HIM. In the end it's up to my dad to say yes or no, which i can almost gurrantee a no, until he's f`ucking already living in the basement. He's just a straight up loser and that's the only thing my mother seems to agree with.

 WUT

I can't exactly communicate with my mother, I feel like anything I say will either break her or make her more ignorant of the fact. I can't put my own foot down, it's not my house, and trust me my sister uses that all the time evidently. I can't exactly call the cops becuase it might hurt more than fix anything and I'm at the mercy of my dad coming home and laying out his authority which won't happen for two weeks.

So do I just lie down and accept my sister is a inconsiderate bi`tch where wishing she suffers such an amount of failure she may commit suicide reasonable?