Good one :P
Nice and funny cartoon. I like the mixture of manga-style and your own style. For example pickletoez' eyes in the square, when you say "Is that so".
Also the details make it complete, the mother who is busy or the little cat head on the babies jacket.
There are only two things I need to criticize.
First off and not so important, the final two facial expressions remind me a little of Kimmy Gibbler from Full House. That's very funny, but I can't identify "you" in those pics. But on the other hand I don't know how you really look (only your drawings) and I don't know how your sister looks in comparision to the cartoon, so maybe I can't really judge it.
Second, the crying baby needs sound, but not in a speech bubble. I think the correct term for what is needed is "lettered sound". I hope you know what I mean. It took me some time to realize it, but I instantly thought something was wrong there.
But don't get me wrong I love the cartoon!
Sistertastic sounds like a great idea. I'm looking forward to it! ^^