If you feel you are growing up and can make your own decisions, then why don't you get a job and get a place of your own so your mother can't tell you what to do. I think as long as you are living under her roof, you should follow her rules, maybe just be polite and not smoke around her. She is worried about
your health. And I know you may be worried about
hers. But there should be some form of respect on your part. You are a visiter in her house in my opinion. And she sees you doing something detramental to your health. Like I mentioned before, I watched my husband die of lung cancer and it wasn't a pretty sight.
But in reality, if you are old enough to make your decisions, you are old enough to get a job and get a place of your own where you only have you to answer to. Be good to your mom. It is mother's day for lands sake. Tell her that you love her. Make her proud of you and happy to be with you.
I am not saying that what she is doing is right either. But she is your mom and does care about you. People with addictions often blame others for it. It is their excuse for their bad behavior. But try to give her a break, she is probably doing the best that she can. And make an example for your brother. Take care of yourself.
Hugs, Karen