Kittens on the roof

I've been trying to catch all of the cats that are here in my yard - nine of them so far - spayed and neutered, to stop the influx of felines. I only had one female left to catch, Misty, but she is the most feral and unfortunately the most fertile. I've been trying to catch her before she had kittens again but just a few minutes ago as I was watching a movie on the computer I heard the high pitched meowing of a kitten. My heart sank.

I went outside in the dark with a flashlight, trying to follow the sound, but it seemed to be coming from the roof. Then I saw Misty running past me with a kitten in her mouth, and as I watched, she climbed up a tree to the roof with the kitten. Then there were more kitten cries from up above. I feel sick. I can't get up on the roof anymore with my bad knee and I can't see very well either, so the kittens are pretty much on their own. I can still hear them. I really really really hate this endless cat situation :(