Forum Discussion
Since they changed to the new genealogy system in Royalty and Legacy, the family trees are actually pretty simple in that as long as the game knows who your sim's parents are, then it builds a tree dynamically by tracing sims back through their parents.
So you wouldn't really edit a family tree directly - there is no "family tree" file that you can edit - you'd go in and change the parent and child relationships in CAS for who you're trying to get to appear in the family tree. So for example if you had a sim and you wanted a great-grandparent to show, you'd have to load up the sim's grandparents in CAS and then add a parent for them.
This doesn't help for lore and existing families, we really need advanced family tree editing. Also, I have encountered bugs where Sims cannot be set as child (option doesn't show) and I do not use MCCC or mods to fix/work around this.
Plus I want this set up in manage world before I start my game, not spend the game going household to household cheating and adding in CAS.