The Sims game should have the option to make some members in a household NPC. Think about it.

It would be interesting to have NPC family members but at the moment the AI seems rather borked for Sims I leave on free will.

NPC Toddlers, children and teens is a challenge I try, which works well with parenting skills and gives the children a sense of personality, but even then the free will AI isn’t that great.