Smokers in my house. Need advice. What do I do? =(?

I would first talk your dad, when you are calm, and maybe bring up the subject by saying something like "I have not been feeling very well lately" and when he asks why nicely mention that you think the smoke might be bothering you, and maybe remind him that you used to have trouble with smoke when he smoked in the house, and that it helped a lot when he started smoking outside. Try to be positive and make it clear that you don't mind your cousin living there, maybe say that you are glad that your family can help them out or that you enjoy their company, but that the smoke is making you sick and you didn't want to offend or upset them bit were really hoping that maybe they could start smoking outside. Ask your dad for his support, maybe see if he will mention it to them for u, or ask him if it is ok if you mention it to them yourself. Hope this helps