Sister,
Heck yeah you are doing the right thing! Good for you for taking these steps!!! Alcoholism is a Family disease so what you are going thru with your parents sounds about 'right.'. I suggest going to the library and reading about the disease of alcoholism and going to Al-Anon.
What you describe you are trying to tell your brother is termed Boundary Setting. There is a current thread on this topic from just this afternoon on this forum. Also, please check out the stickies at the top of the forum. There are distinct steps you can follow to help you communicate your boundaries to your bro.
PS You seem to know this instinctively already, but you are right that you have no responsibility toward your bro Or your family to reward him for EVER being sober. And you are doing the right thing by setting these boundaries. I am truly impressed by your efforts!