Busydaycarelady, my 4 children all started smoking when they were teenagers and I made them smoke outside in all kinds of weather hoping it would slow down their habit. And being teenagers they smoked in the house once in a while when I was at work but I always knew the second I came home. All they had to do was get close to me and my throat closed up. I cannot be around smoke or the smoke that even wafts off clothes.
Once a couple of my children quit smoking in their 20's they realized I was not in fact over-reacting!!! They apologized to me. Smokers really don't realize how stinky they are!!!
So I'm writing this to tell you that I completely understand how you feel. I absolutely cannot BREATHE around smokers and it's kind of important to breathe. Your headaches are REAL. I'm so sorry that your family doesn't understand. Unfortuately, they have a right to their life in their home but can you visit for a short time, take some medicine before you, stay in a hotel instead of in their home if it's a weekend visit, you know, find ways to compromise and yet stay healthy?