I provide the following book suggestion as a kind of spring board to further reading on the subject. The Sociopath Next Door - Martha Stout - ISBN-13: 978-0767915816 is a decent introduction to the susbject, but don't take it as gospel. Martha Stout, through anecdotal narrative, attempts to provide those of us not exposed to a bit of psychology with some perspective into the behavior and motivations of the sociopath. It's a good read, certainly an eye opener, but shouldn't be mistaken for a research paper. She, in my opinion, is writing more as a science journalist then anything else.
Not a sociopath, but having known 2. I would recommend reading this book, it explains a lot: http://www.amazon.com/Sociopath-Next-Door-Martha-Stout/dp/076791581X
Seriously, read this book to understand the condition a little better: http://www.amazon.ca/Sociopath-Next-Martha-Stout-Ph-D/dp/076791581X
I read this, thought of a couple craptacular people from my past and had a ding moment.
I may say some things that I feel you need to hear, but may not necessarily want to hear. I'm not trying to be rude; I'm trying to get my message across. Here goes.
Life is about things you can control, things you can't control, knowing the difference, and knowing what to do about it.
Factors that are outside of your control are not worth investing your time and mental energy into, because you can do nothing about them. Instead, focus on factors that you do have control over, and work to modify those. You will be more effective and will waste less energy.
How do we apply this to your situation?
Your sister is, very likely, a sociopath. I am not a clinician, I am not a professional of any sort, and even if I were, diagnosis through the internet would be ridiculous. But based on what you've presented here, she seems incapable of feeling love for or obligation to others. If she is a sociopath, nothing you can do will change her. You may manage to find some ways to cause her to try to become more covert with her behavior, but you won't be able to address the root problem. I recommend reading <em>The Sociopath Next Door</em> by Martha Stout.
The TL;DR is, if you're dealing with a sociopath, the only way to handle the situation is to create distance. Remove yourself from the sphere of influence of this dangerous master manipulator so that you do not become intentional or collateral damage.
Your parents are in some sort of codependent relationship with her. They don't want to kick her out on the street, because she's their child, and they don't want to see any of their kids out on the street. They fear for her health. They know you will be alright, because you've demonstrated the capacity to be an independent, functional adult. She hasn't, so she needs their help more, from their point of view.
Sociopaths are very perceptive - many of them spend a great deal of time studying human nature so that they can manipulate optimally. In this case, she's aware of where's she's 'got them' (their fear for her safety) and can cut right to the root of the issue by threatening suicide to get her way, if necessary.
You cannot control your parents' actions. They are sane, rational adults who see what is happening, understand the situation (to some degree), and yet are choosing their behavior. You can't change that.
So you need to make peace with it and move on.
Write your Mom and Dad one last latter. Along with the letter, enclose two books. <em>The Sociopath Next Door</em> and <em>The Gift of Fear</em>. The former will help them to recognize sociopathic behavior. The latter will help them to recognize he tactics dangerous people use to gain, maintain, and manipulate their trust.
Once you've done that, you've done all you can. Let it go. Have the best relationship you can with your parents, enjoy your time with them, and don't let the situation between your parents and sister trouble you.
Your mindset also needs work. You're in your mid twenties at least (I estimate), and you're still in competition with your sister. It's ridiculous, it's a waste of energy, and it needs to stop.
Here are some quotations from your post:
>she moved with them... I live on my own,
.
>That's right, I can't move in with them to try and better myself, but she gets to live there rent free, and doesn't help out with any bills.
.
>she also has her $120 cell phone bill paid by my grandmother. I pay for my own.
You're an adult. Get over it. Your parents and grandmother don't love your sister more than you. They've just been manipulated into believing that she needs their help more.
Which is fine. They gave you food, clothing, and a roof over your head for X years. They don't owe you anything. You're on your own, you're doing fine - make peace with this and let your resentment go.
Summary:
Things you can't control:
What your sister does.
What your parents do.
What your grandmother does.
Things you can control:
Whether you have a good relationship with your parents.
Whether you have a good relationship with your grandmother.
Whether you feel stress and anxiety about your family treating your sister differently than they treat you.
How successful you are in life.
Invest your energy where it's most productive to do so. Make peace with the rest and move on. I'm sorry you're in this situation, and good luck.