They all seem to be warming up together. Randi is much less tense in Nibbler's presence, and Pixel has started playing with her! I still keep them all separated at night and during the day, I want to make sure that the two bigger cats a) get a long with Nibbler, b) know that they are not to play rough with her (Pixel seems to understand this, but I'm not sure about Randi as they haven't really played yet)