AITA for not allowing my sister to come to my birthday party with her boyfriend?

My sister (23F) and I (25M) were both raised in a very religious environment and we both left Christianity as soon as we left our parents house. Last year I came out as gay and this year my sister came out as polyamorous and she started dating a guy and his girlfriend.<br><br>She has repeatedly said things like “wow, I can’t believe we fell for that stuff” or “I can’t believe I used to think like that” about Christianity and the toxic things we were taught to believe, mainly about lgtbq+ people.<br><br>My birthday is next week and my boyfriend and I are going to celebrate it with some friends and his family (who have basically become like a second family to me).<br><br>My sister asked if she could come too, with her boyfriend and his girlfriend and I said yes. Then she said “I know this is gonna sound weird but…. I’d like to bring my boyfriend’s ex girlfriend as well, she is like a sister to me and to her boyfriend’s girlfriend and him, and she was one of the people who helped us break free from the religious stuff we were raised with”. I said to my sister “I don’t wanna be mean, but why would I want someone who was in a relationship with your boyfriend in my birthday party, when your relationship with them is so new (only 8 months)? And why would he want that too” and my sister said “well she’s like part of our little family, and it wouldn’t feel right if she wasn’t there. Also, you’re doing all of this to celebrate coming out and leaving that toxic Christianity stuff behind. It’s not a regular birthday party and she’s part of the reasons we aren’t Christian anymore”. Her and her boyfriend and his girlfriend have been calling me bigoted and intolerant for not allowing his ex to come. They’re saying the ex is part of their little family and it’s polyphobic to exclude her.<br><br>I don’t really care about the poly thing, I’m only upset because I don’t want the ex in my birthday party. AITA?<br><br>Edit: thanks everyone for your comments, I really appreciate your help.Sadly I can no longer answer manually because it got too crowded. <br><br>Please know that the birthday party is not to celebrate that we’re poly/lgbtq+ (even if I’m gay my sister is not) but to celebrate us leaving that toxic Christianity stuff behind. Also, his ex is not “part of the family” just because she happened to be with him at the time in which they met the person who helped them leave that stuff behind. That logic applies to me and my boyfriend and his family because they were the ones who helped me. Which is why they’re invited.<br><br>And for the people saying I’m forcing my boundaries on them I wanna say.. I just didn’t want the ex at MY party. I didn’t oblige my sister and her boyfriend and his girlfriend not to have other relationships outside of the three of them. It is absolutely reasonable to not want the boyfriend’s ex at MY party.<br><br>I did not come here to bash the poly community, I’m sorry if some of the words written were offensive or hurtful.