In order to have a well sourced individual we need names, dates, places, and relationships.
A birth certificate would usually show the relationship but lacking this it sometimes takes multiply source documents to establish the relationship.
I have thought about creating a new event/fact for relationship to allow me to enter how I think this person is related to their parents. I have in the past sometimes used the name source to show this relationship by adding conclusions. I have sometimes used the birth event to show the relationship and also placed conclusions in the birth event.
None of what I have tried seems to work well but I am leaning toward using a new relationship event/fact and within this place conclusion statements based on why I think the relationship is correct.