Am I wrong for disowning my brother bc he basically dump one of his kids on us(me, my husband, and my mom) doesn't come around at all and I don't want to take care of my nephew anymore

So almost a year ago, one of my brothers baby mamas got in contact with us because she was leaving a bad situation and starting over in her life and she needed someone to keep my nephew until she could get on her feet. My first question to her was did she get in contact with my brother to see if he could take his son, or she responded with he told her to call me. So some backstory, I am the oldest of my mom's two kids. I've always been the more responsible one out of everyone in the family. I'm also a mom of eight kids: 6 biological mine, 1 amazing bonus baby, and our god daughter that we are going to adopt soon. I love kids like since I was a kid. I've been crazy about kids. I have no issue with taking care of kids whatsoever. The problem is that my brother didn't even try to take his own son, automatically push his responsibility over to me and as a result, my mom also. I also want to say that my brother is I want to say like the golden child or my mom's favorite it's been like that forever. I used to be real hung up about it, but I met my husband and honestly I could care less because I have a beautiful family and a man that loves me. I don't have to be anybody favorite because I'm theirs. I told her no that I don't feel like I will be able to do that just because I already had a lot on my plate. She then went to my mom and my mom agreed to take in my nephew, mind you my mom lives with me. I was not happy about this whatsoever And when asked why couldn't he say with any of her family until she could get on her feet, she just basically say none of her family wanted him. I felt bad, I so agreed to help my mom take care of him but only for six months because she should be on her feet by that time. My brother had agreed to make sure that he bought what my nephew needed and also send money for him every month. This was at the beginning of summer. My brother has not sent much of anything for his son during this whole time. He's only came to see his son twice since he's been living with us, and he doesn't call to check on him whatsoever. My mom doesn't have everything she needs to take care of him like access to his medical insurance and stuff like that. Me and my mom and my husband have been doing everything out of pocket for him and begging his mom for the information for him. She ended up joining the military so she's gonna be gone another year. My brother literally went no contact with us two weeks before Christmas and no one's been able to reach him. The last thing me and him talked about was why he's not taking care of his son and he told me it was because he was making sure that his brand new baby girl had everything she needed. I disowned him right then in there. Some background on my nephew, I'm not sure what trauma he had living with his mom, but this baby has a lot of trauma. It's to the point that we need to see professional help for him because there's nothing that we can do. He likes to fight my children and he steals. He lies whenever he's caught doing something wrong and he's constantly stealing from everyone in the house to the point that we have locks on everything. We never had to do that before. It is now to the point that I no longer want to help take care of my nephew because it is affecting our finances and our children. All of our kids avoid him because of how violent he is towards them and they constantly tell him to leave them alone because they know it's gonna be a fight or he's gonna take something of theirs. Am I wrong for feeling like this about my brother and nephew? I just really need some advice because this situation is causing such a issue in my whole life. My mom is telling me I'm just giving up on my brother, but I feel like he gave up on his child. Sorry in advance for the run on sentences. Just any advice would be helpful