Mother of Believers
The wives of Prophet Muhammad - أمهات المؤمنين - were the women married to the Islamic prophet Muhammad. Muslims often use the term "Umm al-Mu'minin" prominently before or after referring to them as a sign of respect, a term derived from the Quran. Prophet Muhammad was monogamous for 25 years when married to his first wife, Khadija bint Khuwaylid. After her death in 619 CE, he over time married a number of women, most of them widows, for reasons of family bonds and to provide for them after his companions had died.
There is no evidence that the wives of the Prophet (S) or Fatimah al-Zahra (A) covered their faces.
Face-covering (niqab) became common among Muslims around or after the time of the caliphate of Imam 'Ali in Kufa, and so it seems reasonable that his daughters and those who came after them covered their faces since this was a social norm then at that time, at least for women of certain social classes.
(This is of course based on historical records we have of that time, and God knows best.)