Hi Cathy,
I am dealing with the same issue right now in trying to quit. I am a college student, and am living with my Mom who is a smoker. She knows that I am trying to quit and have tried in the past, yet anytime I give up and crave a cigarette, she will always give one to me. She even smokes inside of the house, and no matter how much I try to convince her to smoke outside (would help her smoke less too!), it IS her house and I can't make her do this.
The best success I have found is in trying to express to her just how important this is to me, and how serious I am about it. If your sister and your bf love you and know how much this means to you, hopefully they will be able to refrain from smoking around you, at least within the first week or so while you are really experiencing the withdrawals.
In all reality, you will have to find the strength to deal with being around smokers, in your personal life and out in public places.
A friend of mine who quit shared this odd technique with me. When someone lit up around him, he would purposely stand near it, and just smell the smoke, (probably considered 2nd hand smoking!) and he would let that be enough for him to satisfy his craving. I've tried this a few times, and mostly it has only made me want to smoke one myself.
The other thing that sounded helpful was what I found on this site about triggers. For coping when friends smoke, it suggested waiting 5 minutes while they smoke before lighting up yourself. Then the next time increase it to 10 minutes. I think what this does is trains us to break the "every time you smoke, I smoke" cycle. This is suggested to be practiced before the quit date though.
Let me know what works for you, and GOOD LUCK!
-A