“You will not have only one lot.” Joshua is not saying that the tribes of Ephraim and Manasseh will have more land, another lot; but rather that if they take the land that they have been given it will be enough for two lots, as indeed the division of the land into the tribes of Ephraim and Manasseh showed. Basically what Joshua is saying is, “If you take the land you have and fully possess it, you will not have just one lot.”