A: First:
It is not permissible for a woman to show her adornment in front of Ajanib (men other than a husband or permanently unmarriageable male relatives), such as her brothers-in-law, her husband’s uncles, or her paternal cousins.
Second:
As for her paternal grandfather’s sons (her father’s brothers), it is permissible for her to uncover her face in front of them, greet them, and shake hands with them, as they are Mahrams (unmarriageable relatives) to her. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.