AITA for refusing to accommodate my grandkids at my wedding?

I am an older woman (middle 50's) who is in the process of planning my dream wedding. I've always wanted to get married on a beach in a tropical location, and my fiancé is happy with this choice so we are making it happen. <br><br>We don't plan on having a major boogie, literally only parents, siblings, and their spouses, plus kids. I am about 150 pounds and planning to wear a size 6 wedding dress, and my bridesmaids will be my daughters. <br><br>The issue here is that one of my daughters does not want to be a bridesmaid because she will have recently given birth. She doesn't want to be in a bridesmaid dress so soon after having a baby. Then, her sister offered to push back the wedding so that her sister could comfortably participate, and she could bring her baby. I said no because the wedding is already being held on a different date than my preference so that the baby could be there, and am not willing to accommodate them more than I already am. Since I said no, my daughters are angry that I am being selfish and unwilling to accommodate their baby. I am growing very tired of all this and am inclined to uninvite them if they keep this up. AITA?