Actually those would be very good sequel ideas and now that you have me thinking about it, I would assume EF would be aware of their sequel viability and conceivably might even have plot outlines for them, because those would have built in interest for sure.
One of my all time faves and (even though it's definitely a short story) it is one of 4-5 to actually include a young female Loli to tween to teenage girl. All In, the black, white and silver toned comic from Everfire Magazine is the only one to feature (not merely include) a young (14) girl and no young male at all. People Do Crazy Shit For $ pt 1 includes a sister Lizzie (this will be the one of 4 which most Everfire fans will already be aware of) and for which he has published a teaser/sample for a sequel (not to be confused with PDCSF$ pt. 2 which while labeled a "sequel" is a typical shota/mom story featuring an unrelated and not typical Japanese family) in Everfire Magazine. A Stripers Plan is another which includes a young sister but is short. Then finally another very good, but also very short story with a young sister is In A Parallel Universe 2. I know there is a partially color/partially BW Christmas story from EF Magazine which includes a teen sister which is older than the little bro, and I suppose by the most technical definition should be cataloged as a 5th example of that sort of story. My point, of course, is to ask all of you if there are any "younger sister included or featured" stories I am completely unaware of?