I find this particularly interesting. It's in the instructions to modders posted yesterday to prepare for next week's update.
From the Royalty & Legacy Expansion Pack Base Game update, it will not be possible to set any family relations in Python other than direct parental relations and partner relations for existing SimInfo objects. Any other (indirect) types of family relations (siblings, grandparents, cousins, in-laws, step-relatives etc) will be automatically deduced and managed by the new Family Tree Service, and can’t be set directly anymore, neither by code nor with tuning (loots, household templates etc).
Family Tree Service keeps a persistent, always growing family tree graph for all sims in the save. It keeps the data about dead sims even after they get purged from the save (unless they were manually deleted in CAS). It replaced the genealogy_cache entirely. Every node in the graph is either lived or living sim, every edge of the graph is either parent/child relation or a marriage.
On every loading, the game synchronizes the state of SimInfos with the family tree graph in the save and family relbits between all related sims.
Oh my! This sounds like a much needed upgrade, but at the same time quite scary to us playing old saves. I'm so glad I use my own online family tree, so whatever happens to the one in-game, won't affect me total overview.
