This is the Mom again.
I talked to Angela after hearing from several of you regarding the one kittten with the poor leg development. I told her that passive physical therapy was suggested and showed her what was being discussed. I also told her to give kitteh some time as they were only a few days old and lots of things could change. I did not yet show her the video of Charley. I figured I'd save that for later, once I knew how receptive she'd be.
Well, one week later, I'm happy to report that Brownie (as they're tentatively calling her... at least we think it's female) is definitely looking better. The rear legs still look longer than the rest of the litter, but they are approaching a normal shape. Angela says she's been exercising her twice a day when Mommacat goes outside for a stretch.
Angela's still planning on adopting out all of the kittens and not keeping any, and she thinks she has homes lined up already for three. I've already been told that I'm not allowed to bring home any more cats... my family's threatening to call me the Crazy Cat Lady as it is! :D
Thank you all again for your advice and input!