Unveiling before disbelieving relatives

Question:

Is a women allowed to uncover herself in front of her mother's brother or her father in-law if they are disbelievers, people of the book?

Answer:

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

A Muslim woman does not need to cover herself from the persons mentioned in the above question if they are non-Muslims. The evidence for this rule is the saying of Allah: {and not to show off their adornment except only that which is apparent (like palms of hands or one eye or both eyes for necessity to see the way, or outer dress like veil, gloves, head-cover, apron, etc.), and to draw their veils all over Juyubihinna (i.e. their bodies, faces, necks and bosoms, etc.) and not to reveal their adornment except to their husbands, their fathers, their husband's fathers, their sons, their husband's sons, their brothers or their brother's sons, or their sister's sons, or their (Muslim) women (i.e. their sisters in Islam), or the (female) slaves whom their right hands possess, or old male servants who lack vigour, or small children who have no sense of the shame of sex. And let them not stamp their feet so as to reveal what they hide of their adornment. And all of you beg Allâh to forgive you all, O believers, that you may be successful.}[24:31].

The women in the era of the Prophet (sws) used to meet their non-Muslim relatives and there is no narration related from the Prophet that he prohibited it.
Imams Bukhari and Muslim narrated from Asma that she said: "My mother came to me, hoping (for my favor) during the life time of the Prophet. I asked the Prophet, "May I treat her kindly?" He replied, "Yes".

When some scholars say that a Muslim woman should cover herself from non-Muslim women, it does not mean that she should cover herself from her mother, sister, daughter and similar relatives.

Allah knows best.