Assuming there is not something in the more ancient title history, if the two parcels were split into the two homestead sites from a single parcel, an implied easement likely arose at that time. It's possible that a prescriptive easement arose at some time in the past; I would have to speculate about what has happened in the past to be more definite (and guessing won't do you any good). If they have a valid easement, you can expect to bear the cost of relocating the easement.