What to do with my bully brother?

My brother has a sadistic personality and repeatedly harassed family specially my mother. we are cruel with him for many years because of his behaviors. I don't have father. Our new issue is that he don't like my mother's "cat" . he says "i will throw out this cat because cat is pregnant... show more My brother has a sadistic personality and repeatedly harassed family specially my mother. we are cruel with him for many years because of his behaviors. I don't have father.

Our new issue is that he don't like my mother's "cat" . he says "i will throw out this cat because cat is pregnant and its not good for home, we are not Cat orphanage!" but my mother don't have problem with that.

I'm in my mother's side and i think he is doing this only for harassing mom. but if i start arguing with him, It may make things worse and even dangerous. I'm 30 and he is 40. both single.
Update: Where i say "cruel" , i mean upset : we are upset with each other for years. my poor English.
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