How to relieve stress from my family's problems?

My younger sister Sonya who's 8 now is very needy and whiny and she causes stress for everyone because one damn toy is not enough for her! My Grandfather Tony is having chemotherapy because he has cancer from smoking; my mother doesn't have a good relationship with him, but he does with everyone, my (idiotic) pot-smoking 15-year-old father is doing NOTHING but smokes in the basement 24/7!