Sparkplug,
Check this site out this woman has written a book on the Female Brain and also doing work with teens on their emotional balance due to hormones and developing brains. There is a video on one of her seminars and it starts out how your teenage daughter will want to be playing tea party with you one day and the next you are a bitch. My sister is going through this with her daughter right now. The seminar also has part about teenage boys as well. I think you will learn from this, I have ordered the book as well.
http://www.louannbrizendine.com/
I agree that I think you should consider that you will get through this horrible phase in raising a teenager. Yes some are easier than others but it is worth it if you stick it out and I know this will be hard to believe but there are better days ahead, it just may be a year or so from now. I have raised three daughters and one son and each one had its issues. Sometimes it seemed we would never be happy but as young adults the hardest one we can actually laugh a little about the crazinest of it all.
Boys are hard to reach as they don't like the all the words we women seems to have, such as a women will speak at least 20,000 words a day and a man only 7,000, so I found that with my son if we needed to talk or I was trying to find out what was going on it was easier to do it going for a drive, that way I couldnt look at him all the time and he opened up more.
Also, a man is important in a 16 yr boys life, rather than giving him up to your brother, couldn't you think of going slower but having your brother do things with him during the week or everyother weekend having him stay with your brother and let them just hang out doing the male thing. This would give you both space from eachother. Try to work your brother into his life and partially out of yours but you still are Mom and the home base. I think he needs that foundation in you regardless of how far away you both seem at times, his roots are you but he is growing up and its confusing to him.(and you). Check out some online sites about raising sons and glean what you can, but be homebase.
Peace (it will come)
Sheri