This is how I have released myself from the endless anguish of past unforgivable acts by family members:
Calmly, quietly, with closed eyes, I summon the spirit - the very soul - that I am having difficulty with. I acknowledge that there is a bond between us no matter what the hurts or misunderstandings on either side. There will always be love there.
Then I acknowledge that God, the Universe, Karma, or circumstance, put us together for a reason. Whatever it was we were supposed to do, or should have done, for and with each other went horribly off the rails.
Too much toxicity having extinguished any chance for this relationship to become healthy, I release this person's soul from further obligation to mine, and release mine from his/hers. I tell the soul I wish it no harm and hope that the rest of its journey goes well, but I cannot and will not allow its presence in my life. I also acknowledge my belief that when this life is over for us both, a greater power will broker a full healing.
With some people I've had to do this several times over a period of time before I am fully released, but each time brings me a greater sense of peace.