Welcome Chewdat,
Well you are carrying the weight of a lot of people's emotions aren't you? Your parents, your sister's, you BIL (brother in law). I think you are feeling the effects of all this caretaking!
As for your AS (alcoholic sister), there is nothing anyone can do, she has to reach her bottom on her own, she has to want to stop. Remember the 3 C's
You didn't cause it
You can't control it
You can't cure it
You can replace the 'You' in all those sentences with your family and your BIL too. It has to come from her.
That said, you can all begin to heal yourselves. As caring family members/loved ones of an A, we tend to try to 'help' as best we can, problem solve etc etc for the A in our lives, but this does no good, as we unknowingly enable them to continue drinking, and prevent them from feeling the consequences of their actions. All the time spent caring for them, worrying, stressing, it makes us ill, in different ways.
I suggest reading 'Codependant No More' by Melody Beattie. The book is for those loved ones. Alcoholism is a family disease - just look at how your parents are sleepless, your BIL is depressed and isolating himself, heaven knows what the effect of all this is having on that beautiful little boy who is only 4! Time will tell.
You have made a big step for you and your faamily coming and posting here. Perhaps they would benefit from sharing here too? Time to start healing yourselves.
I hope you keep posting, read the stickies at the top of the forums, and get to know us all better. There is alot of experience here that may help YOU.
Love and serenity
lily xxxxxxxxxxxxxxxxxxxxxxxx