If my father touches my wife, does that break her Wudu?

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

The husband’s father is an eternal Mahram for the husband’s wife.  The Awrah of a woman in relation to her Mahrim is all her body except her head, hands and her feet.

The Awrah of a man for his Mahrim is from the navel to the knees.  Therefore, it is permissible both for the man and his Mahrams to look to the other person’s body apart from the Awrah.

All that is permissible to be seen by one’s Mahram is also permissible to be touched, and this does not invalidate one’s Wudu (the touching).  However, if someone touches a Mahram with desire, this is absolutely forbidden whether he touches the body directly or indirectly, i.e. if the body is covered with clothes.

If a person touches the body of a Mahram directly with desire, his/her Wudu becomes invalid, but the Wudu of the person who is touched will not be invalidated.

Allah knows best.