The wonderful (and unique) thing about our two cats, Mitzi and Trixie, is they share responsibility for their two litters of kittens. They each gave birth to three kittens, a few days apart, and soon afterward, began to take care of them together. They groom and feed each others’ kittens, regardless of who they are, and the six kittens play together and sleep together all the time. I haven’t heard of another case like this.
We expected this somewhat, though. Mitzi and Trixie are sisters, and they’ve always cared about each other, although they do argue from time to time. We got them when they were close to two months old, and they’ve been together ever since. They’ve eaten together, played together, slept together — done everything together. I think they were even courted by the same tomcats. Before they gave birth, I recorded a video clip where they were comforting each other, and that’s another thing I hadn’t seen or heard of in cats until then.