Her brother is
    going to marry a corrupt girl and his family want to deprive him of his inheritance
Question

                My older brother has been studying in the
      xxx. for approximately 7 years now.We belong to a very conservative family with strict
      principles. In the last year he has gotten involved(intimately) with a girl who is muslim
      and belongs to the same country except she is very 'Westernised'. They have decided to get
      married except my parents do not agree to the marriage on the terms that the girl is not
      islamic i.e.she doesnt wear conservative clothing, and she drinks, etc..My parents have
      tried very hard to desuade my brother but he has become evn more adamant and is
      threatening to go ahead with the marriage whether they support him or not. Consequently my
      parents have threatened to cut off all ties from him, and cut off his inheritance.MY question is is my brother right to marry this girl with who he is
      intimately involved against my parents wishes?And is it right for my parents to disagree
      to the marriage on the terms i have stated and cut him off his inheritance?
Praise be to Allah.With regard to the question of marriage, if you have any
    authority or influence over your brother and can convince him to give up the idea of
    marrying this woman, then remember that the Messenger of Allaah 
 (peace and blessings of
    Allaah be upon him) commanded the Muslim to marry the woman who is religious. This woman
    is sinful and goes against the religion, she is not modest in her dress and she drinks
    wine, so he should not marry this woman.
With regard to the issue of his disobedience towards his parents, this
    sin is more serious than the one mentioned above. They have told him to obey Allah and to
    keep away from sin, so he must obey them and avoid going against their wishes. Your
    familys rejection of this marriage is quite correct according to shareeah,
    because they are enjoining what is good and forbidding what is evil, and seeking to
    control one who is insane.
It is permissible, indeed it is necessary, to forsake him if doing so
    will stop him from going ahead, because marriage to this woman will keep him away from his
    religion. In America and in other kaafir countries there are many individuals in the
    Indian, Pakistani and Arab communities who have forsaken their religion and are no longer
    Muslim in anything but name.
As regards depriving him of his inheritance, this should not be done
    unless he becomes an apostate (leaves Islam). So long as he is within the pale of Islam,
    and does not do anything to put him outside of Islam or to make him a kaafir, then it is
    not permissible to deprive him of his inheritance, because this is something prescribed by
    Allaah, and as such it is not permissible to change it. And Allaah knows best,