Is “everyone” singular or plural?
Would the noun following "everyone's" be plural? For example:
Everyone's heart sank.
Everyone is a pronoun and means every person or all people. In your example everyone's denotes the possessive form of everyone. Remember that in AmE, it's always singular not plural. So the word following it should always be singular not plural, too. Here are a few examples:
That said, everyone's is also the abbreviated form of everyone is.