They were wearing a mask over their face.
They were wearing a mask over their faces.
They were wearing masks over their face.
They were wearing masks over their faces.
Which is/are correct?
More than 1 person can only wear 2+ masks on their 2+ faces, or no?
Another pair of examples:
Homeowners are those people who own a house or a flat.
Homeowners are those people who own houses or flats.