Okay so I don't know what's going on. I made a Sim and his Brother. One Sim had 2 kids and a wife, and now their relationships are all screwed up. I can't make my Sim the uncle to the children, only B...
There doesn't seem to be a way to edit certain things as of now.
Frankly it's ridiculous that they overlooked changing names after marriage. It's incredibly basic, and it shouldn't take more than a few lines of code.