Does my parents mean to make me feel bad?

Im the oldest of 6 kids being a junior in high school and I might not be the best kid but im not the worst. My dad was diagnosed with cancer 2 years ago and because of that came the many appointments and also anger. I know my dad is frustrated because he cant do many things because of cancer and my mom is very busy because of appointments but they always criticize me and my siblings for not doing enough. My dad calls me things when my moms not home and my mom seems to take her frustration out on me criticizing whatever I do. It bothers me a lot and sometimes I want to snap back and say something but I know I would be in serious shit. I feel like im not a good enough child so can someone give me tips to do more.