Ramban on Matot Masei - Cities and Name Changes

We examine exegetical comments by Ramban on two different pesukim in Mattot- Mas’ei. First, we look at something strange in the lists of cities, formerly in Sihon’s kingdom, which were settled by the people of Reuven. After two names of such cities, the Torah states that the names were changed. Were they changed from idolatrous names? If so, why aren’t the new names recorded, and why are only two cities singled out? Ramban, disagreeing with Rashi, has another explanation: the cities had their former names (from the time of Moav) restored. What is the significance of this? And is the command to inherit the land and settle it a practical sequencing suggestion, or is it one of the mitzvot?