It is easy to write someone you dislike into a one-dimensional villain. While this might be initially satisfying, this approach doesn't serve your final manuscript or help you to sound like a reliable narrator.
Try this writing prompt to better understand those you haven't (yet?) forgiven:
Write about yourself from the point of view of someone who disagrees with you. Maybe you hold a grudge against this person or haven't forgiven the person for something. This exercise is meant to help you see that person's point of view and present the person as more of a three-dimensional character. Try to sympathize with this other person and show that person’s motivation.
Do this for ten minutes without stopping and then re-read what you've written and underline the main ideas. Don't worry about grammar or punctuation as you're writing. You might even simply write down a list of words or sentence fragments. Focus on the ideas, rather than the sentence structure.
Perhaps this won’t fit into your memoir, but it will help you to better understand the situation. You don't have to forgive the person; after all, I'm not a therapist doling out free (and maybe bad) advice. In order to develop the character, you do need to try to find some insight into his or her motives and emotional state.