Hum... you need to check their permissions.
When you move a NPC to your home, you get several options.
Inspect (which lets you see their details), Jobs (assign them a specific job, with bonuses depending their fetishes), Inventory (equip them), send to Kate (cosmetic changes), and Permissions.
This one lets you control them (if they're slaves), from who/with to have sex, meals and clothing etc, and "house in their free time" or even "city freedom" (they'll be roaming around the streets).
Also, setting with who" sex, lets you assign them bewteen other slaves, inseminate others, or you, which works when they have free time.
(I remember them having a small description when fucking between them , sort of "X and Y sneak into a small room to do this and that", but now it's a "placeholder event", since it's on the works)
LoL!
Playing "vanilla" is playing an original version of the game, sans mods.
If you don't use what the game gives you, you're just crippling yourself, of course you'll get defeated often. If you want it harder, you can always change the difficulty on the game's options!
The game is currently on 0.2.11.9, of course you're missing a lot (and might even be playing a non-fixed version).
Submission changed a lot, since now the Imp Fortress have their own controlled areas. Inside the, you'll get overrun by Imps roaming around in groups.
There's also a percentage to run into a powerful Imp Witch and his gang... REALLY though battle, as they throw spells, hits, and seduce attacks, and it's around 4-6 of them. Then it's the fortress themselves, which also have their own quests, and different modes to complete each.
You can use old saves on newer games, but when it's more than 2 updates, I recommend starting a new one, as it might glitch with the new content (and lately there has been a lot of system changes, like new fetishes and perks, and a whole different system of perk assignment for your whole party).
