I would write those letters, then in a little ceremony, burn them. While you burn them let go of any hate or resentment and accept they are c##p people that are best out of your life. Let them go.

I hope this don't sound too bad, but I longed for my mother to love me, longed for her to care, to notice me, to hug me. I hurt so bad, felt so lonely. I tried so hard to make her love me, just to be put down and rejected time and time again.
It was, it did, destroy me.
It had to stop.
So (years ago now) I decided she was dead. I imagined the funeral, the flowers, guests, the cards. I imagined the vicar what she would say. Imagined the cremation.
Mother was dead.
I cried for a month. I had no mother.

Since then I've felt better. No longer do I beg for crumbs of attention, plead for some show of love (that I was never going to get)
I have not forgiven, I can never do that, some things cannot and in my opinion should not be forgiven. But I have accepted that in all but name I've never had a mother. Emotionally I have always been an orphan.

If they hurt you badly it might be best not to contact them. I find abusers, narcissists feed off hurt, the less you tell them the better.

But that's just me.