I (early 30s) have an older sister (late 30s) with BPD. She doesn't carry an official diagnosis, but I'm certain that that's what it is. She's disrupting my relationship with my parents, and I'm not sure what to do.

As a kid, I looked up to her. She took good care of me, but it wasn't until adulthood that I realized how controlling and manipulative she had been. She had done things like breaking up with my boyfriend because SHE disapproved of the relationship, withholding knowledge of a later boyfriend cheating on me because she and I were "fighting" at the time, etc. When she is in a good mood, or if she wants something, she would be saccharine sweet. In her rageful outbursts, though, she says awful things to me, like how she wishes she'd never asked for a little sister. 

When I realized all of this, that I wasn't actually a terrible, stupid human being and that she was a major cause behind my severe depression, I distanced myself from her, and my life was suddenly SO much better. She didn't like this, though, because I wasn't allowing her to control any manipulate me anymore. We didn't (and still don't) speak for months on end. For a time, we couldn't even stand to be in the same room with one other.

Things have gotten a bit better, but she still has frequent outbursts. Despite my attempts at no-contact, I've sometimes gone to her for sisterly advice, against my better judgement. Invariably, she uses the things I've told her in confidence during moments of vulnerability againts me, even during totally unrelated arguments about mundane things ("no wonder you're lonely in your new city and you don't have friends, you're so self-righteous, you don't care about anyone but yourself" etc). When I've told her that her words are hurtful, she's responded that she telling me these things for my own good. So, she thinks that her behavior is justified and will never get help, let alone admit fault or that she has a problem. My overall strategy has been almost-no-contact.

So here's my question. She recently moved back in with our parents, and as such, I don't know how to maintain a close relationship with them. She's a full-grown adult with multiple advanced degrees who should be starting a job, but she hasn't been looking and so is unemployed. I have a full-time job, live somewhat close by, and visit our parents often. My parents are fully aware of her personality problems and are often the target of her outbursts, too, but they absolutely will not do anything about it. I've told them that I'm certain that she has a personality disorder, but they still indulge her, which I think reinforces her behavior. I've even told them that, in the past, she's made me depressed to the point of suicidality, but they keep saying that it's all just sibling rivalry, and they're disappointed that "you kids just can't seem to get along with each other."

In every other way, my parents are loving, kind people and I love them so much. I want to visit them more, but I don't know to navigate my relationship with my sister while I'm there. My sister's presence is deterring me from visiting them. I can't get my parents to visit me, because my sister would get INSANELY jealous, and my parents are not eager to provoke her.

How do I interact with my sister in order to preserve my sanity and not compromise my relationship with my parents? Do I ignore my sister 100%? Do I speak politely with her at all times and appear completely unflappable in the face of her outbursts? Also, do I keep reminding my parents that "this behavior is NOT normal and this is NOT just garden-variety sibling rivalry"? How do I avoid putting my parents in the middle of this situation (e.g., I don't want to refuse to visit altogether, I don't want to force them to take sides during her outbursts/arguments).

If anyone who has been in a similar situation could help, I would truly, truly appreciate any and all advice. I'm at my wits' end. Thank you so much.