Question

can whose be used for plural

Answer 1

Of course whose  which is the possessive form of who can be used for both plural and singular .

ex:

The woman whose dress is black is my mum.(  singular)

The ancient Egyptians , whose contributions to civilization have long been recognized.(plural)

Answer 2

The word “who's” is actually a contraction meaning “who is,” and it is not the plural of any word. So at the end of the day, no, you should not use the contraction “who's” to refer to the plural form of the pronoun who