It sounds to me that there were a number of factors that could have led to you and your brother having BPD. You are reaching out to him and doing the best you can. However, you can not make him change. He needs/wants to do the changing himself. It can be a scary process. And for us (borderlines) its much easier to stay in what is comfortable (even if we don't like it and its hurting us and others) than to make changes. (at least that is what I'm recognizing in myself)

You need to do what you can to make yourself healthy. My parents were a big issue in me getting healthy and staying healthy. After many years of thought and deliberation and talking with my counselor. I made the decision to cut my family of origin out of my life. They were not healthy for me and I felt like history was repeating itself with my girls.

I don't know if that is helpfull or not. I hope it makes sense.