What should a sister, married to a very stingy man who steals to feed them and threatens her with divorce when there are three children, do when she fears for her children and herself from consuming unlawful (haram) things?

If it is proven that the husband steals to feed his family, then the wife should advise him gently and kindly, and remind him of the danger of consuming ill-gotten gains. If she knows the specific haram money, then it is not permissible for her to eat from it. However, if he has permissible money and she can take from it without his knowledge, then there is no blame upon her in that, based on the Prophet's (peace and blessings be upon him) saying to Hind: "Take what suffices you and your child righteously." If she cannot do that, then she should refer her matter to the judiciary to compel him to feed her from what is permissible or to grant a divorce, as Shafi'i jurists have stipulated that a wife has the right to annul the marriage if the husband spends on her from haram sources despite being able to earn from halal means. It is also permissible for the wife to take what suffices her and her children from his wealth if he withholds maintenance.