AITA for telling my sister she can’t bring her kids to our family vacation?

This is my first time posting on this community. <br><br>My parents are going on a vacation and they’re only allowing only 5 people. My brother and I have been saving for a trip so we’re going with them. The rest has to stay home. <br><br>My sister just had her 4th baby. 3 kids is a lot to handle and I know my parents wanted to limit the amount of people going to 5 only so that we can have quality time. <br><br>My sister was obviously disappointed. I tried to explain to her that Mom and dad also want some time off so they can recharge and not be too tired for the rest of the kids. <br><br>I offered to baby sit her kids whenever she needs to go out. <br><br>She said “I still want my kids to come because they need a vacation too.” <br><br>I said “sorry but the spot we’re going isn’t kid-friendly” (they’re going to the beach and it’s not a resort). My sister insists on bringing her kids and my mom said if she brings her kids, it’s only her and the kids. I’ll be omitted from the trip.<br><br>I had been preparing for this vacation for years. I really want to go and I can’t if my sister brings her kids. I refuse to let my sister bring her kids and told her so. Now she’s angry at me and my brother says I’m an asshole for not baby sitting her kids.