Moving a marker pin isn't normal so I'd focus on that. That map you have seems pretty clear so double check to make sure that it is the "official" map that was filed with the city or county when the subdivision was approved. There should be a surveyor name on the map and the developer who laid out the subdivision should know where everything is supposed to be. Subdivisions are laid out by engineering firms who keep records and everything is filed with the city or state. Everything is permitted and filed and checked off when a subdivision is put in so there will be plenty of records. All you are going to need to do is follow the paper trail on where the pins should be and where the driveways should be.

A lawyer could be useless unless he knows something about subdivisions. If it was me I'd start with the developer who laid out all of the lots and see how they wanted things done. That is the plan that everyone should be following. Moving pins and changing land boundaries isn't allowed unless the proper paperwork is filled out.

And in a case like this it is always best to assume that it was an honest mistake. Give the guy plenty of room to fix his mistake, especially if the map is clear. I wouldn't get a lawyer involved up front, just get the pin moved back to where it should be and go from there.