In both cases, the singular is is correct.
When "who" is the question word and there is no subject complement, the verb is singular. This is true even though you know the answer may be plural – many or even billions:
Who knows the answer to this question?
Who speaks Spanish in this class?
Who likes chocolate ice cream?
Who is living in those buildings?
Who on earth is driving all those cars?
When, however, "who" has a plural subject complement, then the verb is plural:
Who are those women in the black dresses?
Who were the winners of the competition?
Who are the leaders of the group?
Who are those people living in that building?
Who are the people driving all those cars filling up the roads?