This is what I do (I've used this a lot):
Click on teenager -> Nraas -> Master Controller -> Advanced -> Family -> Add Parent -> Household -> Select both parents
Unpause the game for the change to take effect, then check the relationship - it should be there now. If not, wait a few more moments. It sometimes takes that for the game to register the change.
Edit: LaPaige, I would have replied before going to bed, but fingers hurt too much. Can I call you next time? LOL
