smatt is correct.
So, there are actually 2 ways to make the NPCs stop covering themselves when naked around each other.
1.
Increase their lust to a point where they're not ashamed anymore. According to the console, the value is Romance, aka lust.
As I explained earlier, the relationship that matters is between the NPC's you want to be comfortable around each other.
So for all NPCs, you use the "all" commands.
Use the following command:
Code:
social romance all all add 100
(I said earlier, than you need to increase Friendship as well. This is NOT true. I just tested it.)
2.
Give them the Exhibitionism personality trait.
Type in the console:
Code:
personality all 100 add 16
Even with 0 Lust, they will not cover themselves if they are Exhibitionists.
You can use both methods if you want, but only 1 is required.
There may be more ways, but those 2 work guaranteed and tested as of version 0.9.3.