We also have a flag shaped lot and shared 800' driveway for our place and the neighbor next door, at out retirement place. We own the bottom (at the town road) and top of the drive before it splits off to each home, and they own the run in the middle, the deed specifies a shared driveway easement for both properties (was owned by one family originally). Unlike most everyone else in the area, unfortunately these neighbors are neither friendly nor ethically employed, so costs for routine maintenance and snow removal are handled individually after a couple years of smarmy haggling and such. It gets complicated because some land is owned by each party, at some places, on both sides of the driveway. I mow everything I know we own, and some land we do not because it is on the side of the driveway our house is on, because they don't maintain it and probably do not know where the property lines are. Although it is an annoying sitation at times, and not ideal, it has worked out OK.
As other posters have noted, establishing clear boundary lines and assuring no installations or use beyond that specified in the easement on your land will be important to get straightend out asap, to avoid false expectations on ownership and property rights into the future.