Go to your main hood, to a family which one of it's members is best friend with one of the lost family.
Phone the "lost" sim, and invite him over.
Then, propose to him to move in (take care that the family has less than 5 members), and take with him his rest family.

After you moved them in, tell the husband to find his own place, and add to him his family. They will be in the Sim Bin, but with 20,000$ only.

You have to buldoze their vacation lot, and their main hood lot.

Bottom line, you have to start with them again. You can use the money cheat to increase their wealth.