Legal Question in Real Estate Law in California

The facts are a little sketchy, and without a credible survey fixing the property line there will be some uncertainty, but here are some tentative answers to each of your questions:

1. The owner does not have the right to charge rent or collect the fair market value against the will of the encroaching neighbor. Remedies for trespass and encroachment are strictly up to the court, unless of course you and the neighbor reach a voluntary agreement and the agreement does not violate any zoning or subdivision law. Changing the boundary between two parcels requires a formal process called a lot-line adjustment.

2. What's happening probably constitutes trespassing. The only issues might be where the property line actually is, and whether thge neighbor has somehow acquired an easement.

3. There are relatively few ways that the rights of Neighbor X to have, hold and use an easement on the land of Neighbor Y can be lost. None of these is likely to apply if the easement has been in continuous use and the nature of the use hasn't changed much.

4. The owner of the easement probably doesn't have recourse against the lender, title policy, seller, seller's broker, and so forth, but might in certain uncommon situations. More likely than not, the person claiming to own an easement on someone else's land must enforce his right against that someone else - legally known as the owner of the servient tenement, the servient estate, the burdened property, or like terms.

Answering this specific question is made a little difficult because "owner" in an easement context can mean two very different things - it can mean the "owner" of the easement, i.e., the party or property benefitted by the easement; or, it can mean the owner of the land uopn which the easement lies. I'm unsure which you mean when you speak of "owner" in your 2nd and 3rd paragraphs. I hope you can apply what I've said to your particular situation.