Not wanting to go to my brother's wedding.

So here's the deal. My brother is marrying a girl who my entire family doesn't really like. We did at first but over the years she just grew into this lazy bitter person. They've been off and on for a long time. They had a little girl before marriage which upset our family. They fight a lot and don't even take care of my niece very well. Every time they want to go out, whether it's going to the store, out to eat, to the mall or hanging out with friends they always leave the child behind. She's had mutiliple jobs and never sticks to it and says she wants to spend more time with the baby but yet she leaves her almost everyday? The house is always a mess and never really cooks. They were apart for about a year and got engaged for the second time immediately. She still doesn't work and demands a new phone, new car, and a new house. To top it off she wants to get pregnant again even though she "has her hands full with the first". She had a miscarriage recently and came to me for sympathy considering I went through one with my hubby and mines first pregnancy. I found out I was pregnant again a few days after she miscarried and she became more bitter about it and is pretty rude to me sometimes. Recently she started high schoolish drama that just topped it off with me not wanting to go to their wedding. All she wants to do is start drama and complaining about what she wants and not having money for anything or the wedding. I was willing to help but she wasn't greatful for it and was still rude to me. Is it wrong for me not to attend to their wedding?  Here's the deal breaker too, I never was close with my brother because he molested me when I was younger. It was an ongoing thing and didn't speak up to my parents about it. My husband knows about it and supports me. I terrified for my niece because of what he did to me. I know relationships aren't perfect but theirs is just too much. My mom supports me of not going because they upset me so much. Am I in the wrong?