It seems like you are really trying to help this person out. However, I don't believe anything that this "brother" of yours is saying. He is as confused as you are and perhaps that is why you chose such a public form to bring this up. Obviously, you will be made fun of when you are involving the entire internet to comment on your brother's situation.
Bus mera aik he sawal hai yahan, maid ko dainay kay paisay nai hain aur dosri shadi kernay k hain? Yeh logic koi samjha do mujhay.
Also, he should divorce her first wife, remarry and start a new family if that woman is in fact so evil. This seems to be the only reasonable solution unfortunately. Whatever happens to his sister is all in Allah's hand. Clearly, even if we takes a second wife, his sister's husband won't take kindly to it either so you are screwed either ways. May Allah make his life easier.