How do I get maxis made families back?

I have an idea that might work. First, open up a brand new save and enter the lots where the desired premades live. Then take the family into cas.fulleditmode and from there SAVE them into your "My Library". That way when you go back into your current save you should be able to access them and place them back into your game. To prevent them aging and dying off again, go into the gameplay menu and select "aging on for active household, only". That way your family will age, but unless you play the other households, they won't. Best of luck. Hope this works.