Your fears and worries are valid, but that doesn't make them reasonable or justified. Assuming you have a good relationship with your family, you were taking your daughters to a very public event, filled with people that your sister personally vouched for or that those people vouched for, and you would have been right there with your girls. Plus you backed out at the last possible second, causing significant stress and logistical issues for everyone else, when you could have told them you weren't going to bring your daughters days or weeks in advance. I'm saying this gently, but you genuinely need to seek help. Living with this amount of your unfounded anxiety isn't going to be good for your daughters developmentally, and it isn't pleasant for you.

By keeping your kids away from the wedding, you created your own bad situation you were so worried about. YDI.