"We do not sleep in the bedroom."
Translation:Nie śpimy w sypialni.
I'm afraid that you clearly got one word quite wrong. "pokui" is not a word, you mean "pokój" (Nominative singular) or one of its cases (see them here).
"Sypialni" is the Genitive singular from 'sypialnia' - meaning the bedroom.
"Pokój" is simply 'a room', any room.
If this sentence was "We do not sleep in the room", that would be "Nie śpimy w pokoju."
I cannot think of an option when it pairs with Genitive. This is Locative and it's the most common situation. When "w" just means "in", "inside", you use Locative.
There are also situations when it takes Accusative, like with days of the week (and the word 'weekend'), and when it denotes some... movement 'into' something, although English won't necessarily use 'into' then.