All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
You are obliged to remind the widow of your deceased brother of Allaah and warn her against taking people's property without legal right because she knows that the house -as you said in the question -is a shared property (between her deceased husband and his brothers).
In case she does not accept your advice and insists on taking the right of your brothers by law, then you are permitted to only take the similar amount that is seized by her, from her husband's business in order to compensate your brothers who had lost their share in that house. If any money remains after paying the rights, then you have to return it to your brother's wife and his children.
However, some scholars are of the view that it is forbidden to do so as the Prophet said: "Give back the trust to whoever has entrusted you with it, and do not cheat whoever has cheated you." [Abu Daawood and At-Tirmithi]
Nonetheless, the preponderant opinion is that if a Muslim can take his right back, then it is permissible for him to take it as the Prophet said to Hind Bint 'Utbah [when she inquired about what she could take from her husband's property without his consent or permission]: "Take what is reasonable and sufficient for you and your children." [Al-Bukhari and Muslim]
Allaah Knows best.