try this...

next time you say something innocuous and she gets very angry with you, do not react to her anger, ask her WHY she is angry at YOU. She may not realize she is taking things out on you, and anyways it kind of sounds like brother and mother need to be on wellbutrin.

If you outed yourself as a smoker, you have to act twice as cool and grown up as you really are to get them to be ok with it and prove it's ok for you to do. Testify.