AITA for refusing to save tickets to my graduation for my stepmom and stepbrother?

I graduate high school in a few months, and was told that I'm allowed 10 free tickets for family. Other tickets are available for purchase. Recently, my father asked about tickets and I told him about the free ones. He claimed that he should get five and my mother's side of the family should get five to make it fair. I told him that under normal circumstances I would agree, however there are only three family members on his side that I'm offering tickets. The three are: my father, my grandma, and my grandpa. The rest are: my mother, sister, stepdad, brother-in-law, and three grandparents on that side. He claimed this was unfair, and that I needed to un-invite my stepdad and brother-in-law in order to invite my stepmom and stepbrother. I said that if they would like to attend, I have no objections. But, my stepmom does not want to go and has been separated from my father for months. For background context: she's left us three times before. This time, she kicked my father and I out of the house instead. Also, she has started the divorce process. I now currently live with my mother as my primary caretaker. Back to the story though. My father called me selfish, disrespectful, and said that my stepfather and brother-in-law were not even family. He also said that my graduation day is not about me, it's about the people who raised me, so I had "no right" over who is invited. I disagreed and told him so. He said that if I didn't invite my stepmom and stepbrother, he would not be attending, nor would he allow my grandparents on his side to attend. He then called me a disappointment and dropped me off at my mother's house. It's been 5 hours and he's now calling and texting non-stop saying I need to apologize to him. Am I the a-hole?

Update: Thank you guys so much for the reassurance that i'm not insane lol. My mother agrees with you guys and I plan to ask my sister about the situation in the morning as she had to graduate high school when my dad was married to our mom so she's seen the worst of his behavior before. I will definitely call my grandparents in the morning, but should I call my dad as well? I'm a little worried that I let him down because he's still my dad. A little more info about my stepmom and father though: My stepmom adopted my stepbrother from another country when he was 2. He is 9 now and my father never adopted him as well. My father has only been married to her since 2020, and he idolizes her. It's strange how perfect he thinks she is. She's fake, hates me, and despises the fact that i'm wlw. I've lived with my dad as my primary parent since I was 6 up until 2 years ago. This was for no other reason than 6yo me wanting to live with the "fun parent." Everything was fine until he married her and he's slowly gotten harder and harder to deal with. Overall, I'm just wondering if I should call my dad and finish the conversation tomorrow morning, or if I should leave it and act like nothing happened.

2nd Update: I tried to call my father to calmly explain my actions and apologize for ignoring him. He didn't answer. He is currently ignoring me because he's upset and acting out. I have tried to handle this is a non-childish way, but this man is no adult. My grandparents having answered me either, so i'm worried he's already got to them. It's been 24 hours and this man is unemployed. There's no way he hasn't been able to get to his phone. I'm going to limit contact as much as possible. I can't deal with him anymore. Unfortunately, due to shared custody and court-appointed calendars, I am not able to refuse visitation. Especially since i'm still a minor. Not only that, but I have to spend 9 days with him starting after Christmas. Now I don't know how this will go down but it's not going to be pretty. If anyone would like an update later if he contacts me please comment and i'll get on that.