I know it's been a while since you posted this, but I recently somewhat solved this problem on my own. I had to use testingcheats, but I was just glad it worked! My family was 2 sims, so I added a random sim to the family. Then I went into Edit Town Mode. When I did this it acted as though it was a brand new game and took me to the 'choose house for these sims to live in'. I chose a random one, and when my trio of sims moved in, I had the randomly added sim drop out (just in case it hurt the other sims) worked for me! hope it helps others.
