Pooja,
Maybe I can tell you who spoke for me. I had ( I can go back any time I want or need to) an advocate/counselor who only represented me. No one else, just me. I think since your mom is not getting good advice, you may need one too, for your Brother and Sister.
See, people need to know that little people have rights too. I thought it was too much religion for me, so I was lucky I had the advocate/counselor. The advocate will speak up for you without getting into trouble, they also let you know that little people have rights.
The right to be free from harm (your parents cannot hit you).
The right to be free from verbal abuse (they cannot call you names)
The right to be free from duress abuse (telling you the world is going to end or telling you stuff about food).
The right to be cared for, a home, food and school.
The right to be happy (this means if you don't want to go to the centre you don't have to).
The advocate tells your parents that if they learn they are causing you harm they will have to answer for the harm. This makes everyone really cooperative and things get better. Also, the advocate tells you to have big people that you can go to for comfort like an aunt or an uncle if you are having any problems. Some one old like fifty or maybe forty years old because the advocate is not always around and they give you phone numbers too, but I never needed them.
I know I have some old ones to talk to and one that knows about this Gyan stuff to. I can ask that old one about the Gyan stuff if I need to, only I messed up my e-mail just about two weeks ago. But I can get to him too. You can also ask your teachers for help. My teacher was really nice to me and understood.
I also, have one old one that helped me (with Gyan stuff) but I don't know who that is, I think he is really old. My parent found that one for me, but I don't know that one, my other parent does.
My advocate is very nice, you can get one too. They represent only you, only your needs, no one else and you can tell them to tell things to your parents if you are just not ready to. Your Brother and Sister shouldn't be worried or afraid and your mother should not hit you, or your dad or anyone (that is abuse). Oh, yelling is verbal abuse too

. The advocate arranges family meetings too, only they have to bring one that represents them but not all the time. So, ask about an advocate and maybe they can help you too.
Bye,
Seva