Thank you for your comments. We're pretty sweet on our girls too. We got Sophie at 9 weeks of age when our other cat (then a different cat) Hannah was 13 years old. This turned out not to be a very great idea, since we really didn't know what kind of creature kittens were since we had only adopted adults up to that point. Hannah died only about 4 months after we got Sophie, and I'm afraid getting a kitten did not help her at all at that point. Nevertheless we had Sophie, and loved her, and she is growing up to be a fine furry feline (we say that Hannah even taught her to wrap her tail around her toes, since these are the only two cats we've had that do this!)
Once about a year had passed, we got the old "second kitty" bug again (okay, well, I did, and convinced the family.) We adopted Roxy, intentionally looking for an adult cat, since having a true new kitten was way more work than we knew. As you all know you do not choose your cats, but your cats choose you, and Roxy's story of abuse captivated us, especially because Roxy (age 3 1/2) seemed not to be at all afraid of us, and we knew she needed us. She has been a super cat, but has turned out to be alpha around here, and it has been a little surprising to us to see our perky little kitten become the shy pick-on one.
We hope they begin to get along better in the future, but Roxy doesn't make life easy for Sophie some of the time. No doubt you'll see me hanging around the "behavior" thread for a little wisdom on these two!