A: It is not permissible for women to uncover their faces in the presence of their brothers-in-law because they are not Mahrams for them; they are in-laws.
The Prophet (peace be upon him) was asked about Al-Hamu (the in-laws of the wife - the brothers of her husband or his nephews etc.). The Prophet (peace be upon him) replied: Al-Hamu is death itself.
That is, the bad consequences of uncovering their faces in the presence of them are more harmful because it is treated leniently. (Part No. 17; Page No. 400) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.