Unfortunately, as a general matter, there is right of rescission--so no right to change your mind and void the transaction--for the vast majority of purchases, leases, rentals, service agreements, etc., unless and only to the extent that the seller lets you do this (i.e. that the seller has a policy allowing the buyer to cancel within a certain time). The exception is a mortgage for a residence, which comes with a 3-day right of rescission; but car leases do not have this.So your in-laws are probably bound by this agreement unless:1) They can show that there was fraud--basically, they were lied to about something important, to get them to sign up;2) There was some significant and mutual mistake--basically, the two parties didn't quite each understand what the other was saying, and so there was no meeting of the minds; this is very hard to show, however;3) The deal was illegal--i.e. the dealership did not have title to the car, or the car is not road worthy; or4) The in-laws lacked capacity to sign a contract--but showing they lacked mental capacity (e.g. Alzheimer's, dementia, etc.) is obviously not something they can or should do lightly, since it will affect their whole lives.