ridiculous stories about how she was ostracized, victimized etc and we were all jealous of her as she "was the most like our Mum" who had just tragically died suddenly at 62..
Something - a bit of objective analysis here from someone on the other side. When someone dies suddenly, a parent, also with your family history of early parental death, being made NC by a sibling can be as bad as being bereaved again.
Exactly this happened to me. New relationships were forged between less close family members who then ostracised me to cover their actual poor behaviour (eg excluding me from important death related proceedings that I had more right to a say in than they did).
All kinds of shit happens when there is a close and a sudden death so you do need to be really forgiving, people do and say stupid things, other people come on the scene, you might be too open or too closed with them, your feelings are not straight - I consider bereavement to a temporary madness and reasonable decision making is very hard, especially when new people come into the decision making process.
Fact is you lied to your friends to cover up what your sister said, hoping that going NC with sis would ensure the lie wouldn't get back to them, am I right? This is what's probably lost you your closest friend, not your sister's disclosure. Not blaming you for this, it sounds like it was a mess with confidences breached etc and you wanted to do what was the right thing at that time for everyone. But the pain of being excluded when you are still grieving is immense and is akin to being bereaved all over again. I'm not saying you pander to your sister but start from a point of understanding that perhaps she's not as narc as you think she is, but desperate to get her family back.
It might be that she isn't narc at all - that's why she keeps pursuing you. A true narc would write you off as 'unusable' or 'no longer fit for purpose'. I am of course projecting here because exactly this happened to me and ironically the true narc is the one who made me NC and engaged the rest of the family and turned them against me. I have been forced to play the long game, ie wait until time passes and the truth reveals which I know it will. DB is finally warming towards me again after a period of out of character tragic and shocking coldness. Meantime I keep my distance for fear of being branded 'controlling' or some such other narc trait.
Sorry to ramble on about my own situation but I think bereavement is a time when terrible things can happen but it is temporary and needs patching up sometimes.
Of course it will get to your DS what happened to his auntie, the truth always comes out and it will be confusing. I have had to back right off for fear of messing with the little one's heads even though I know I did nothing wrong. I have even told them as much, that I will see more of them when they are older etc because my involvement in his life right now is difficult (but always there if you need me kind of thing) - no doubt that action in itself was read by the narc as some kind of manipulative thing to say - whatever I do or don't do is read like that because it's convenient.
What someone else wrote upthread about allowing them to deceive us is interesting, will pick up on that later.
Anyway this is a really interesting discussion I don't mean to sidetrack everyone.