Okay thanks. I've checked online bur there seemed to be some contradictions about tombstones and everything I've been able to find is about played households. So I guess that since I didn't play them, I won't be able to get their stones and thus the seance will not work for my family.
My child, Gideon bought his paranormal badge from the traits and rewards so I am curious about how it works. He's a human surrounded by occult siblings so he is naturally curious about the supernatural.
As for finding anything online, again everything seems to be centered around played sims. I'll do more research though.