AITA for refusing to babysit my soon-to-be step-grandkids anymore?

I’m 24F. I have 2 full siblings (MF) and 3 half-siblings (3M). <br><br>My father is remarried to a woman “Candace”. Candace has 2 sets of twins: 4 girls total, who are ages 2 and 4. Candace and my father are expecting a child together. Candace has a very hard time managing her 4 girls, and my father was so understanding to the point where he asked me and my 4 siblings to babysit her kids while he treated her to a spa day for her birthday. The original plan was to rotate who babysat the 4 girls for a weekend each month, with the idea that Candace could go and do whatever she wanted while my dad watched the kids. <br><br>A few months ago, it became apparent that although there are 5 of us, my dad and Candace only seemed to ask me to babysit. I am the only single sibling who doesn’t have kids. My brother and his wife have 2 kids. My sister and her husband have 2 kids as well. My half-brothers are all single but two live out of state and the other is a wanderer who rarely stays in one spot for too long. <br><br>I told my dad and Candace that I had to stop babysitting because it was unfair to expect me to do it every time. Candace offered to pay me, but I told her I didn’t want her money, I just wanted my weekends back. My dad suggested that Candace and I swap; she watches my dog on weekends I go camping, and I watch her kids on weekends she needs to. The thing is, Candace has never watched my dog. I have asked her 4 times since we made the arrangement, and each time she tells me she’s too overwhelmed with her kids. This brings us to the present. Candace asked me to babysit the girls this weekend because she and my dad are going out of town. I told her no because I already told her I wasn’t going to babysit anymore. She asked if I would just take the youngest two, but not the older ones because they’re difficult. I refused. She then offered to pay me double what she was offering before, but I refused. The older twins are difficult because Candace is a lazy mom who lets them do whatever they want, do any activity they want to, and lets them play on their tablets until they go to sleep. But that’s not my problem. Candace told my dad I was being selfish and uncaring because I wouldn’t babysit. He said it was true, and if I was the only sibling available, it was selfish of me to refuse. I told him it was not my job to raise her children, and he told me I should be happy to help my stepmother out because she’s too overwhelmed. I refused, and Candace called me up crying telling me how hard it is to be a mother to so many and how she thought I would be more supportive as a woman. I apologized and told her I couldn’t babysit, and she called me a selfish asshole. <br><br>AITA??