My big sister just died as well as my baby cousin?

I am 7 and my big sister Julia who was 10 just died as well as my baby cousin who was 3. why did they die in the same week? and how can i go on? i have tried to find comfort with my daddy and grandma but they just tell me to get over it and make the most of my life, and when i cry they tell me to shut up and grow up. my mommy died when i was 3 and my big sister was my best friend and i looked to my baby cousin as a little sister. *cries* so what do i do? i feel so alone in the world.