I believe that there is a transfer function in the menu of those units. It has been awhile since I have played with a Navnet 1, but they definitely have it in Navnet VX2, and the units are very similar. You just have to be careful, because if you have different waypoints/routes in each unit, you will overwrite the units you are transferring to. it is best to enter all your waypoints/routes using one unit, then transfer to the other units.
i'm just some idiot from the internet