AITA for canceling my brother's wedding venue reservation without telling my sister-in-law?

I (25F) own and run a family-owned small business that manages several vacation properties. We own them all and we renovate them every 2 years to keep them up to date. It's a family affair and we all work together. I work full time outside of the family business and my older brother and sister (by 4 years respectively) handle pretty much everything else. My parents started the business before they passed away in a car accident when I was 17.<br><br>Recently my brother signed a pre-nup that allows him to keep his money and assets should they get divorced, unlike if he would have signed a traditional one. His fiancée is a family friend and has been staying at our properties since forever. She met my brother while visiting one of our properties and they hit it off. My brother decided he wanted to use our business to book the venue for their wedding. It's an intimate ceremony with only family and closest friends. They picked a date just over a year from now.<br><br>Here comes the slight issue: this date is a complete coincidence but it's the same date as the annual family reunion. We moved it to this date 7 years ago because apparently a lot of our family are getting older and traveling is harder for them. It was supposed to be a one-time thing, but for some unknown reason my brother and his fiancée wanted this date and everyone else was expected to accommodate for it. I found out about this 2 years ago and I made my wishes clear: I would not be attending and I wanted the venue reserved in my family's name so I couldn't be booked for anything else on the same day. My brother and his fiancée had no problem with this and my siblings agreed with me on this.<br><br>Yesterday I got a call from one of my coworkers telling me that my brother tried to book our venues for the date he got married on, but I had already reserved it for myself. I had just finalized the booking a week prior and I had paid the deposit already. He was denied and when he kept being an ass about it, I stepped in to resolve the matter and he accused me of trying to interfere with my brother's wedding. I told him to piss off and he hung up on me.<br><br>I was upset and I told my sister and he what happened and she lost it. She said that I was cruel for canceling the reservation and that I was being an asshole for ruining her dream day. I asked if she knew about the date and she said she didn't but that my brother was furious that he couldn't book the venue and he berated me over the phone. My sister cried to our other brother and he stepped in and told her to shut the fuck up and stop being a bitch. He then called my brother to tell him that the venue was booked under my name and my brother started yelling at him and hung up on him.<br><br>I'm conflicted on this issue because on one side I did not want to attend on this day and I made it clear to my brother and he had no problem with it, but now that I think about it, maybe I was being an asshole for canceling the booking without giving him the chance to change the date.