AITA for skipping Christmas with my in-laws because they didn’t invited my sister?

My (33m) sister (31f) is autistic, mildly disabled, she functions completely normally but is socially awkward and can have difficulties with certain tasks. My parents passed away a few years back and it’s just been me taking care of her. She lives with me and my wife (33f), and my wife is very kind to her. <br><br>My in-laws (Husbands parents) are very kind as well, my father in-law is a bit of a grump but he’s always been nice to my sister. My mother in-law is just the nicest woman on earth. My brother in-law and his wife are also very kind, they all love my sister. <br><br>This year my in-laws want us to spend Christmas at their house. I contact them about it and assume they meant myself, my wife, my sister and I said sure. Then they told me they didn’t mean my sister as well. I was shocked, I asked why not, they said it’s a family Christmas for their family only. I told them my sister is part of their family as well, they said she isn’t. <br><br>I told them that if my sister isn’t invited, we’re not coming. My wife agreed with me and we’re both not going. They called me an asshole for not coming to Christmas because of my “petit” (I have no idea what that is but it didn’t sound nice). I think it’s terrible that they don’t want my sister there, and I don’t want to go without her. Am I really the asshole?<br><br>Edit: I just want to say, thank you so much kind strangers for the awards, I honestly didn’t expect my post to get any. I just wanted an honest answer to my question. I will make sure to give them out as I see them. And once again, thank you. <br><br>Also, thank you for the gold, silver and platinum, I reads all the comments and I appreciate the vast support my family and I have received.