Are the 10-year-old toy cars are safe for a 2-year-old?

Given that your child is two, there are several items of concern:

Paint toxicity. You could do a bit of research on this based on the manufacturer's info that's likely imprinted in the base of the cars.

The bigger thing to worry about it is choke hazards created by small parts. If the wheels, doors, or windows on the cars aren't affixed solidly, then they could break off and your son could try to swallow them.

Whether you put them in storage or try to sell them is up to you, but it sounds like you'll all be better off if these cars are put out of sight and out of mind.