I agree, for the parents to through you out of the house - that just goes to show how deep their denial is. It seems they really do not want to deal with this - because then it becomes a REAL problem.
I think it is great you wrote the letter - you were able to write out your feelings and this is therapuetic and it helps you.
I do not belive your letter will make a difference to these people. You do not have to prove anything to them - you are all adults.
If it makes you feel better and gives you hope send the letter to them, but I have a feeling they do truly know your side of the story and know what you are going through they just don't want to get involved.
It is so much easier to turn the other way and do nothing.
For a long time I dealth with my mother in law not being involved because she knew I was always there to pick up the pieces and "Keep him alive" - she always assumed that if I was around nothing terminal would happen to him. At that time my job was to try and keep my husband alive rather then be a wife.
Yes it is fantastic to have the support of your inlaws and his friends and family, but that is not always the case.
For 3 years my AH sister did not speak to me becuase she thought I was a horrible wife that would not allow her brother to have his own life....only now after recently things were so bad with his addiction did she apologize and let me back into her life and has actually been a huge help to me in dealing with the issues of his addiction.
It is so hard and complex to understand why people react the way they do. I say this is your son, your brother - don't you want to help? But ultimately the addict is the only one that can help himself. It is great to have the support from friends and family, but it just does not always happen.
Keep your chin up. take care of your self and don't worry or stress out to much about his family. they are not going to help you....only you can help you.
Please keep us posted on what happens.