The samples BTConnectTest and BTReceive show how to communicate between two NXTs.
Both robots could use SimpleNavigator to calculate their positions as they move around and the first robot could send its position to the second. SimpleNavigator uses dead reckoning so is not that accurate. There is no sensor that will give you an accurate location. leJOS supports GPS sensors but they are only likely to be accurate to within a few meters. If you want greater accuracy you need to use localization algorithms like the Monte Carlo Localization classes in lejos.localization but these need a map of your room, are slow, quite difficult to use, and not that accurate.
The leJOS developers are working on improvements to navigation and localization.