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mortgage vs car loan vs invest extra cash?
user
a point that hasn't been mentioned is whether paying down the mortgage sooner will get you out of unnecessary additional costs, such as pmi or a lender's requirement that you carry flood insurance on the outstanding mortgage balance, rather than the actual value/replacement cost of the structures.  (my personal bugbear:  house worth about $100k, while the bare land could be sold for about twice that, so i'm paying about 50% extra for flood insurance.)  may not apply to your loan-from-parents situation, but in the general case it should be considered. fwiw, in your situation i'd probably invest the money.
assistant