Is there a cooling off period for rental agreements?

No, unfortunately there is no cooling off period here.

Best advice is to have attorney write to owner, indicating this is extenuating circumstances, no judge will hold you to the lease, etc. and the owner has to take reasonable, diligent steps to re-rent the home at comparable rate and term, and only until that is complete can the owner even have any quantity of damages to come after you for. By then you will be moved, and owner will never collect anything. The letter from the attorney should detail this all out and make offer that the owner keep deposit as damages, since it is likely first and last and settle this all up front. Owner cannot hold you to 30 months damages. With due diligence he can re-rent in a month or 2 or 3 longest. The attorney letter would clearly spell this out. I do advise an attorney write the letter not you since it will obviously be taken much more seriously. Perhaps 1-2 hours attorney time.. Very sorry about your wife's' mother.