I think that if you still have the code written down for your last adult's parent, then you go to the 'Grandparents' house and input it there. I'm not totally sure about this, since I've never tried it, so I'm sorry if that's now how it works. .
Edit: Or, maybe it's was cho_jinsei just said. :kuribotchi: .
Sorry cho_jinsei,I tried that before but it didnt work. But it has to be the fourth generation? or did you mean to say 4 years old? ^_^ Anyway,I STILL dont understand,guys. Sorry.