Finally, there was a sticky grammar and usage issue in which the pronoun has to have the same grammatical number as its antecedent. "Their" is plural and "everyone," its antecedent, is singular.
Finalmente, había una difícil cuestión de gramática y uso en la que el pronombre tiene que tener el mismo número gramatical que su antecedente. "Su" es plural y "gente", su antecedente, es singular.