How to find a lost Parent Sim?

I have a sim that got married to another sim. They have a son now. So I was looking at the Father one day and looked at his genealogy. He has a Mother and a Sister listed in his Genealogy. They are green when I click on them. They are not ghosted out or empty, like a culled sim. I assume they are alive in the game some place. How do I reconnect with them? 

I am willing to use a cheat but I would have to know their Sim ID or something like that? I don't know what to do. I think it would be cool to reintroduce him to his Mother and Sister and let them meet their grandchild finally.