The genetic data for many of the Strangetown sims had errors in it, but it was corrected with a later EP, so I didn't do anything myself. I just happened to have the updated version of the Smiths, where the DNA is not completely messed up.

I think you can fix it in SimPE, even if you have an earlier version. It's not really hard, but I'd recommend reading a couple of SimPE tutorials first.