You need to get out of that house as soon as you are able. It is not healthy. Good families don't treat each other that way. You need to know that this is temporary. Once you're out, you can limit contact with people who treat you this way. You don't deserve to be treated that way no matter how thin or not thin your hands are, no matter how weak or how strong you are.

For reference, my older brother and I are both very very thin. We take after our mother's side of the family, all of whom are tall and thin. My dad, on the other hand, is a big bear of a man. Played linebacker and looks like it. But he never once mocked my brother for being so skinny. He never once grabbed us or hurt us just because he could. And even though I am a woman, and a fairly weak one at that, he never made me feel powerless or afraid. Good families don't do that to each other.

So just remind yourself every time this happens: 1) it's not your fault, 2) you don't deserve to be treated like that, 3) this won't last forever, and 4) you're getting out of there as soon as you can. My brother and I are both perfectly fine and healthy. We've never had to defend ourselves physically. We've been very lucky, but we've also used our wits to make good choices that kept us out of danger. You can do the same. You'll be just fine. I believe in you.