The game doesn't recognize second cousins, brother-in-law etc.

The family trees could definitely add more to gameplay with some new options. I'd also like it to be easier to add to family trees when creating a new sim too. For example, while back I decided to create parents for a sim and move them in to the neighbourhood. It worked in the end, with the cas.fulleditmore cheat, but really I think it should be possible as standard option.