AITA for wanting to say to my father that I don't really care about his happiness?

I know am not the asshole. I just want some perspective, maybe take this out of my chest. Maybe even some advice. Me (F, 24) and My father never been in exact good terms. My mom (55) and father (58) split up when I was 2, divorced when I was 3, so we never had the conventional father/daughter relationship. I used to visit his house every other weekend and spend two days with him and his wife, and eventually, his new kids, he paid the minimum child support (we didn't starved mainly because my mom worked day and night to support us) so he wasn't that involved. When I was 10, my mom sit down with me and told me the whole story about the divorce. It was necessary because my father is toxic and a liar, so she knew that if she didn't done that soon, he would've twist every part of the narrative. Basically he cheated, a lot. They were married for 13 years and he cheated for 12 of those years. After the divorce she found out that he had numerous mistresses. He traveled a lot for work so that help to cover up his lies. He even got engaged to a woman in another state, while married. The father of this person found out and contact my uncle latter. I have two older siblings (F 34 and M 31) That means that every year that my mom was pregnant with his children, taking care of his house, helping his family, e etc, He was fucking around. Besides being dangerous for her (for the diseases he could've transmitted to her) we are pretty sure he had other kids during their marriage. Once I even got mistook for another girl who is the youngest daughter of one of his old mistress. I am 80% sure she is my biological sister (somethings was said about it in the past, it isn't just a theory)... I never said anything cause she doesn't live in my country anymore and we don't have any connections or contacts so I never reached out. And honestly I don't know if is fair to drag someone else to this mess. Anyway, after many situations that took place in his house, with him and his wife, calling me fat, stupid, lazy, rude, ugly and many things you could imagine, I realized that, if I never come to his house, our relationship would eventually died out. I was 12 and basically start seen him once every 3 months. That was more than enough for me, years passed and we just wasn't close. It was easy. But once close friends and family realized that it wasn't just me being rebellious cause of my age and that I was really more happy without him in my life, they star hold him responsible for this failing on the family. So he start make me guilty about it, making me feel like I was missing important milestones and family contact for being stubborn. I was 18, and caved in, became close again. Even introduced my boyfriend at time to them. Every interaction was painful, I struggled. When the pandemic started we got isolated and distantly again and due to political differences, I blocked him. You guys can imagine what was his Political alignment. I simply couldn't accept. I blocked him for two years. He didn't had any access to me or my life. Also a very easy thing for me to do. Eventually, he reached out trough people close to me, to tell me that the distance was making him depressed, that he was getting sick because of this stress, that his marriage was falling apart, everyone was blaming him and all that he wanted was to make amends. It was all lies, of course.But I agreed to meet up, and I told him everything That I knew he was always lying, how he never supported me or my siblings and throwing that responsibility on my mom almost killed her, how he was never around, how he was negligent, toxic... I told everything and his response was that he was young, naive and he did what he thought it was best. He didn't apologize. He felt like I had no reason to blame him. He is selfish and honestly doesn't want to hear other's opinions. That cathartic moment for me meant nothing for him. I don't know if he is narcissist or what but I ended up feeling completely empty. It was pointless. I was done talking and trying. I unblocked him so I don't have to hear about it anymore, and for the last years I've been polite, treating them like every other person that I know. But never let them being close enough to really mean something. I don't fight back. They invited me over several times. I just decline. My siblings have a close relationship with him and, In they're own way, let all of it die with time. But I'm kinda of his karma. I'm the last missing piece on his perfect family portrait. And I absolutely love that. Recently I've been working on my younger brother's school. So I see him twice a week. He's a great kid (12) and I love him very much (would never blame a kid for his parents mistakes). My father's wife also work on that school and I avoid her at all cost. She came to my classroom the other day and interrupted my lesson to invite me for father's day. I answered that I wasn't sure I could make it (I didn't celebrate with them on the last decade, even though my siblings always insist for me to go). Her response was that it would've made my father 'so happy'. Am not clear enough? I don't care about his happiness. I don't care about his sadness either. I don't wanna have any attachments with my father and his wife. So, would I be the asshole if I told them that? My mom thinks that if they didn't realize yet, either they don't wanna see it on my actions or they simply would never respect my wishes and boundaries. I don't know if they think that they could eventually win me over or that if I'm polite they still have a chance. Should I try to say it one last time? Or I would I be losing my time and stressing out for nothing? I probably won't say anything unless they contact me again. But I still felling tempted. Probably won't have updates. Just wanna see outside of my box. Sorry if it's too long, I'm unpacking 20 years of unnecessary drama. Should I let it go? And also, may be confusing but English is not my first language, you can (nicely) correct me in the comments. Thanks for reading ♥️