@vyvexthorne If they are a relative it should tell you that when you open their Sim profile, unless that isn't working for you right now. It works for most relationships but the ones I'm not seeing are step and in law relationships.
I agree with you though, I have ageing actually turned off in my game and have very complex family networks.
I think they missed something when adding family interactions. They should have made it easier to identify and bond with extended family members. Instead we have "Joke about family heritage" which is just so ill thought out. We should have something to acknowledge familial relationships. I'm not seeing anything like that in my game, unless it is part of GRO.