Just a couple of thoughts.
First, thanks for all your posts and responses. I understand all the comments about boundaries and how important they are. For me, I think the key to establishing and maintaining boundaries with your NPD parents is understanding that once you do so, you will give up hope of having a relationship with those people. In my case, I do think it's very true that my NPD parent did not regard me as an individual, but merely as an extension of herself. They do not regard you as an individual and so there is no "you". That is hard. Whether it's with my NPD mother, co-dependent dad or "healthy" brother, I know the reality is that once I enforce boundaries, any relationship with them is gone because I need them and desire relationships with them much more than vice versa. I will then be literally alone. I really am alone now but in a more superficial way. Either way, it is painful.
As for the co-dependency issue, I'm still not sure about that one. I guess it depends on how you define it. I put together all this information for my "healthy" brother in the hopes that he could understand NPD and really so he could understand me. I guess I was selfishly hoping for a little empathy and compassion, something I never got. I was also hoping that he would understand that there really was something wrong in our family and that my depression and issues were not all my fault.
I think that's the hard thing with NPD. Since the NPD person will never consent to therapy to get an official diagnosis, it's usually just a case of the survivor's opinion. I begin to doubt myself. Is this truly NPD or am I just blowing all these things out of proportion? It's that validation that I need so desperately for so many reasons that I never get that is so disconcerting.