A true easement is on the deed or title and automatically goes with land. Look to the deed and title to see if there is one; look up the other property's deed or title in the county office, too, to see if there's an easement on it. If that's not the case, then your parents only have a "license" (permission) personal to them to cross the land, and such a license is NOT transferrable unless the property owner states it may be. If it is written in "their names" it is likely such a personal license, since as stated, a true easement goes with the land and has nothing to do with the specific owners.If, as is likely based on what you write, this is a license, not easement, you need the other owner's permission to transfer it. If he/she withholds permission, if the land is totally landlocked, you can likely get a court to grant an easement by necessity--to use its authority to require an easement be created because there is no other way to get to the land. This would require going to court, if the other property owner fights it, and could be expensive.