The household net-worth is the furnished value of the house plus the money they currently have.
To check furnished value of the house, go into build/buy mode and look at the furnished price. Then add that number to what they have in cash.
Home value + Cash on hand = Family's net-worth
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If you want to be sure what the net-worth of the household is, evict them and move them out without their house. It will send the household to the clipboard. Click on them to see their net-worth.
** It is recommended to do this with a copy of your save-game. That way the household doesn't loose any wishes they may have in the current game.