No step grandparents in the sims 3?

Jeansoo

Hi, I’m playing 3 generations in my game. I stopped my sims aging up because I don’t want to see them dying from old age. So T sim has 2 sons and Y grandson. Y is also young adult. T sim’s wife died from jelly bean long time ago, and newly married with an adult guy is called M. I’m playing with Y grandson and his uncle J who is also one of T’s sons. A few days ago, Y sim met his step grandfather at the supermarket. Suddenly, his step grandfather gave 2 flowers and was flirting with Y. I was surprised and the relationship was set to just a friend, not to step grandfather. Is that normal in the sims 3? If there’s no step grandparents exist, then I will set them as grandfather. I don’t want to see any affair in this family.