Does a son in the game have to have a father-son relationship in the "favourite personal" tab or it's just based on last name?

I have a player in my youth acadamy who shares the same last name as my manager character, but they don't have any type of relationship between them. I know some players that are brothers and they do have "Brothers" relationship between themselves in the "Favourite Personal" tab, and I haven't seen any "Parents" type relationship at anyone at all, no matter who I checked on that I know their father works in proffesional football and is in the games database