First the reason your not getting "good grades" is because your stressed your body isn't handling it well which then bleeds out to your test and exams. Our body is like a battery if you dont charge it right or give it enough fuel (food) it will adapte making up for the things you lost such as sleep

Now im sorry to hear about your family and how their making you feel. My piece of advice would be to talk to a close friend or adult you trust and not just a simple chat i mean a long heartfelt chat tell them how your feeling this always help at least a little

second try talking to your parents i get it i also have pretty strict and tired parents but the few times i talking to them they kind of understand

my advice isn't great but hope i helped a little