@SimGuruNick - I uploaded two full saves folders to the same link, so you have your pick of files 🙂 This is a legacy challenge, so there are multiple generations here.
In "Timothy-child", the two elder sisters (Georgia & Gabriella) see the child traits for their nephews (Lane, Wyatt & Martin). Georgia, the eldest, sees the child trait for her younger sister Gabriella. Everyone in the family sees Timothy, the child, with his "Mean" trait.
In the "Timothy-teen" file, the relationships and traits seen remain the same, but Timothy aged up (by game-no cake, autonomous aging). His traits are Geek and Mean, but everyone in the family sees his traits as Mean and Wild (his toddler trait) - EXCEPT his little sister, who was born when he was a teen. She sees his adult traits.
This is base game with RG, Holiday & Grim's guitar. No cc or mods, never used. Never used cheats to age any of the sims; have never used CAS full edit mode, have never changed any of their traits from what I gave them.
Can't think of any other information to share, if you have any other questions I'm happy to answer. Thanks!