Tish, I am so very sorry for all yo have gone through. I haven't experienced anything so first hand as this myself. But I did watch my own mother go through it with hers.
It broke my heart to watch her lay herself open to this abuse over and over in the hope of some kind of closure.

Firstly,you will never get what you need from a narcissistic personality. She will never say sorry or admit she was wrong.

I know this because even on the day she died my gran blamed everyone else. With her final breaths she condemned my mother to a lifetime of mental anguish because she would not tell the truth even at the very end.

Please don't do this to yourself. My mum has never been the same, she was the baby too,her brother and sister,like yours had long absolved themselves of any part in the chaos,except if it suited them.
My mother lives burdened everyday somehow wondering how she couldn't make this woman see the truth of it.She wanted answers for the cruelty she had suffered over her entire life.
And ally grandmother did was exclaim how we had all ruined her life.

You won't find what you need from this woman.I am so very sorry.

Please take care of yourself for your boys. I know my mum didn't mean to break my heart but it happened anyway. We had wonderful relationship for the most part.
But she still bears the scars from the final days she spent in her mother's company.

I wouldn't wish that on anyone. For your own sanity don't Hope for her to suddenly need to put things right before the end.