As in the prior comment, here’s the usual disclaimer - I am not an attorney and therefore cannot give legal advice or interpret law. But maybe I can give you my layman’s perspective, and help you find the laws that may apply to your situation.
I have two thoughts here. First, much would depend on how the original right of way was written. I'd want to see both the deed that created the easement, and/or any Plan on which it appears, and also the deeds to the properties that have been able to cross that last piece of land. Were they actually granted deeded rights to cross that last piece of land? Or was it just assumed by them, and allowed by the owner of the last parcel? If the owners of the other lots were actually deeded the right to cross the last parcel, then the new owner cannot "correct" their deed and thereby extinguish rights that were deeded to others. But if there were no specific rights granted, then I believe they would be within their rights to clarify that permission to cross has been withdrawn.
There is a series of laws on "paper streets" that clarifies who owns a road that was laid out in a subdivision plan but never accepted by the Town. They are 23 MRS sections 3027, 3027-A, and 3030 through 3035, and Title 33 sections 460-475, especially 461 and 469-A. Here are links - use the arrows near the top right of each page to scroll through the sections that follow.
https://legislature.maine.gov/legis/statutes/23/title23sec3027.html
https://legislature.maine.gov/legis/statutes/23/title23sec3030.html
https://legislature.maine.gov/legis/statutes/33/title33sec460.html
The owner of the abutting land probably has a valid claim to the land under the road, but then there’s the question of whether others have any easement rights to pass over that land.
It's a bit ambiguous, but 23 MRS section 3031 (2) says:
2. Private rights. A person acquiring title to land shown on a subdivision plan recorded in the registry of deeds acquires a private right-of-way over the ways laid out in the plan. If a proposed, unaccepted way is not constructed within 20 years from the date of recording of the plan, and if the private rights created by the recording of the plan are not constructed and utilized as private rights within that 20-year period, the private rights-of-way in that way terminate.
Unless title has been reserved pursuant to Title 33, section 469‑A, when the private rights established by this subsection are terminated as provided in this subsection or by order of vacation by the municipality, the title of the fee interest in the proposed, unaccepted way for which the private rights-of-way have terminated passes to the abutting property owners to the centerline of the way.
But does that mean that everyone in the subdivision has a right to use ALL of the road, or just that everyone has a right to use the part of the road that provides access from their land to the public road system?
The Town could have reserved its rights to accept the road if they had renewed their option in 1997 and again in 2017. (23 MRS sections 3031 and 3032.) Finding that out would require either asking the Town, or going to the Registry of Deeds website and searching for Miscellaneous filings by the Town in 1997 and 2017.
Second, can the owners of the other parcels claim prescriptive rights? Establishing such rights would require going to Court to prove that they and/or their predecessors-in-title have used the path across that last parcel for twenty or more consecutive years without interruption, without the permission of the landowner but with his acquiescence, or that their use has been "so open, notorious and uninterrupted that acquiescence will be presumed." But if the use was by permission, that will not create an easement by prescription no matter how long it continued, because the use was not "adverse" to the owner. The owner can revoke permission at any time. (That may be what has happened here.)
Unfortunately, even if permission was not specifically granted, it's generally assumed that recreational use of another person's land is permissive use. There was a court case, Baptist Youth Camp v. Robinson 714 A.2d 809 (Me. 1998), in which the court ruled that an easement was not obtained by adverse possession or by prescription because the use was permissive, and was not continuous. I suspect this may be a similar situation.
One thing you could try is bringing in a professional Mediator to approach the new owners, listen to their concerns, and see if some sort of agreement can be reached. It’s likely that they want to preserve their privacy. But there is also value in preserving good will with one’s neighbors. What concessions can others make to help? Is it possible to establish a new walking path in a different location so they don’t have people walking through their front yard? Or are they just dead set on ending all passage? MARA has had Leah Boyd, from Clarity Services, do two training sessions for us on skills for conflict resolution. She specializes in group mediations.
One other consideration - are these year-round residences, or seasonal residences? If year round, who provides snow removal, and where does the plow turn around?