Oh, that's so wonderful!!! I hope that my kittens will feel that way about me someday, too! As for your little sister, the behavioralist that we spoke to said that cats are not like dogs in that they don't want to please their owners, they want to do what pleases THEMSELVES. Here are some of the things our behavioralst told us to do for our anti-social cat:
1. Never initiate contact, but allow HIM to initiate.
2. Have set times during the day when we interact with him by feeding treats (wet food with gravy) and having play time. Make him come to us when we have something for him to eat, and - if he will - have him sit in our laps (holding the food in our laps and having him climb up there, not picking him up and putting him there.)
3. Once he's used to having interaction during those set times, start petting him while he's eating and while he's playing. Eventually, he'll come to associate your touch with something he really likes. He'll also (supposedly) start to seek our your attention during the times you've set for interaction.
I'm no cat expert by a long shot and so far these things haven't done much for our anti-social cat, but he has improved a little bit (he'll hang out with me early in the mornings, for instance.)
It's worth a try, anyway!