Hi Tim's Sister:
I'm not trying to be funny, crass, or make light of your situation but I thought I'd share this with you. I was reading your post out loud to my daughter (who's sitting at the table next to me), and her response to your question, "Is 12 beers a day too much?" was, "Is 12 pieces of cake a day too much?" And while she intended her answer to be funny, it really drives home a point. Is twelve of anything too much? Twelve sodas? Twelve pieces of pizza? Twelve chocolate bars?
My answer to your question would be yes, twelve beers a day indicates there's a problem to me. But that's just my own opinion. What matters more is does your SIL think 12 beers a day is too much? Has your brother's drinking caused her family distress? Have 12 beers a day brought chaos into her life? Have 12 beers a day prompted her to call you in desperation?
I think you already know the answer, and that's why you're here. The other posters have given you wonderful suggestions on how to help your SIS, how to help your brother, and how to get started on the road to recovery.
We are here for you. We are here for your sister. And we are here for your brother, if he chooses. Welcome to Sober Recovery. You're among friends.