If I got a case worker and she say I can't live with my adult brother, is that true?

Another question, how old are you?

You say "adult brother" does that mean your under 18? If so, if brother wants you to live with him, then he is the one who should be doing the request. We really need more info.

She says you cannot live with your brother beCAUSE..........................................what?

We really need a lot more information than what you have provided. Come back and explain in deeper detail and you'll get the help you need.