You choose the options for one main character, and the other will answer based on their AI personality. If there is a difference you can not always determine who will win, short of reloading (the first person who answers can change their mind), though Charisma can help.
You can start off with a trait pair one way and change it answering the other way enough times, which will change the bonus.
You can change the AI personality at a certain point in the game (in the room in the homestead opened after the end of time).
