One cannot tell “a” what he or she can tell someone else regrading “a”‘s property unless it impinges on your property. It’s annoying, but true. Unless someone is breaking the law or a City ordinance of some type, you have no recourse. I HATE shared (for all practical purposes) driveways. It’s really best to have a definite line of demarcation, so there is no confusion. I would paint a yellow bus stripe down the middle or plant something, just to clairfy the boundary.
