Can a post nuptial agreement be rescinded? We signed a post nup five years ago to separate assets that I had from my grandparent

I would suggest you sign a new agreement to rescind the previous one so it is clear, especially in case any copies of the post-nup are found in the future. You should consult with a local attorney about how to do this properly so it is effective.

You can rescind the agreement but it needs to be done in writing, usually in the form of a separate agreement. You may want to speak to the attorneys who helped you with the post-nup in rescinding it.

You're best advised to do a brief modification of the prior agreement to make clear that you're recinding it. God forbid you tear up a copy you have, and then another one re-surfaces at some point in the future. Schedule a consult with a Family Law attorney in your area.