Gender and number and pronoun agreement
It’s fine to avoid a clunky “he and she” / “his and hers” construction by using “they” / “their” with a singular pronoun antecedent.
Each passenger should check their tickets before they board.
Fiction character sheets
Please provide with your manuscript a separate document listing key people and places, with key details about them.
This will help ensure consistency, so the protagonist’s older sister remains throughout the manuscript the same height, with the same hair and eye color, visible marks, birthday, and food preferences.
Likewise the yellow Cape Cod style house with green shutters and a cedar fence across the street will remain that way unless something in the story changes that.