Since my life is currently so full of kittens, I figured I'd post another update!
As of two weeks ago, the kittens are no longer broken - they've both been fixed. I was intrigued to see that spays are now done via laparoscopy, so the female only has a tiny wound on her abdomen, barely larger than a puncture, instead of a several-inch long incision. They both felt better soon afterwards but it was hard trying to keep Kella from *not* jumping and playing while her innards mended. Henry's surgery was much less invasive and he came away with a shaved bum, an empty package, and a wobble in his walk until the anesthesia completely wore off.
They're 4.5 months old now, and are getting more used to us. Henry readily comes up to us wanting to be petted, and he will often let us pick him up. He headbutts with such enthusiasm that I'm half worried he's going to give himself a concussion!
Kella, on the other hand, is more guarded, shy, and skittish. She comes up to us to be petted while we're laying in bed, often at way-too-early o'clock in the morning, and really wants attention at that time. But most other times, especially during the day, she won't let us pet her, and if you move too quickly she'll just run and hide. All we can do is be patient, and try to earn her trust.
Kella and Henry are adorable, though, especially as they stalk and pounce upon and run after one another. It's a lot of fun watching them play together.