Hey, I just found both stories this week. Saw this one first, and when I started to read it I realized I had no clue what was going on. Fortunately, as I was working my way backwards through the stories I found your other one. Really enjoyed reading it (was really nice not to have to wait to finish it too ... lol), and I am enjoying this one as well.
One question came to me as I was reading the most recent chapter. It appears that Samantha knows about Sarah wearing diapers and such. I don't recall a scene in which Samantha finds out, but even if it is just considered an "out of story" scene, wouldn't there have been some reaction to this news on Samantha's part? She knows Jessica wears them out of need, but for Sarah it is sheer pleasure. Even the most open-minded person would probably pause for a moment hearing that, and Samantha doesn't seem like the most open-minded person. ;-)
One other thing comes to mind - what's with all the "everybody changes everybody else's diaper"? I mean - it's a nice fantasy, but is it plausible? Maybe at least with Jessica, who seems to never change her own diaper, an explanation would be a good idea. Something like she finds it is always easier to have someone else change her, or when someone else changes her the diaper is always adjusted better (something I have found to be true) or something to that effect.