Wow, I'm truly touched. I have been in a similar situation with my mom, and two brothers for the past 15+ years. I haven't pursued the issue much lately, mostly because of fear on my part. I think that I'm afraid of stripping them of something they feel is a "necessity" if I get them to see reason. My sister is really the only one I have any kind of real relationship with. She is baptized, but does not attend meetings or anything. Of course, it would seem to me that she has the best of both worlds...the worst my family can say to her is "you really need to go to the meetings." Once they make sure they throw that in the conversation, they can associate freely. My father, who has never been a JW, once requested that a picture be taken, during a get-together at my sister's house, of the entire family (all his children) and insisted that I be a part of it. My brother called me shortly thereafter to remind me of why he couldn't be a part of it if I were there. His main reason seemed sincere..."how can I teach my children one thing, and do another?" he said. I didn't know how to argue that one. I guess I'm a bit weak, when it comes to this kind of stuff. Needless to say, any pictures that were taken during that get-together excluded yours truly. It is sad.
When my sister got married, a few years back, she asked me to give her away. I was thrilled...my mom wasn't so thrilled. Neither of my brothers attended the wedding, one giving a somewhat believable excuse, and the other being pretty blunt about the fact that I would be there. My mom did attend, and months after the wedding I had the chance to go back to my hometown, so I asked if I could stop by just to say hello. "You know you can't, and you know why." was the response. She then wrote a very detailed letter to me with all the reasons why she didn't want me to come by. That was the only time I had the guts to actually write back with any real conviction. Unfortunately, I was probably not as tactful as you, but I did tell her that I would accept her disowning me if, and only if, it was her decision. I would not accept it if it were based merely on the decision of some organization. She never replied.
Anyway, thank you for letting me ramble. I'm very glad that someone has the strength to keep at it. Your letter is very well written, and very well thought out. I think it is very encouraging. One of these days I'll have to try again. Good luck! I hope things work out for you!