I just want to know if when the big sister shows up, that means youve gotten all the little sisters in a level. I thought it was, but when I pause, it still says "little sisters on this level: 2". Just need to know for sure before i take this train, cheers!

well how are the pictures?
The ones that hasn't been taken have a picture of a little sisters head and a tunnel or something, they be smiling if you saved them, and yucky if you killed them.

If it's two little sister icons, that  means you've allready got em.
 
If it's two icons of a little sister and a big daddy, that means they're still out there.