^
I agree. I think they'll only be going to the end of volume 4, which is probably the best place to stop.
Here are some upcoming episode summaries from KmY (was posted there a couple of weeks back. Translating the titles, but I'm leaving 7's in Japanese only)
Episode 8 There's no way my little sister could (get this kind of anime adaptation) (= replacement for last chapter of volume 3)
Episode 9 There's no way my little sister could be this into
eroge (???)
Episode 10 There's no way my little sister (would cosplay like this) (= first chapter of volume 4)
Looks like they're cutting the plagiarism one out? Which doesn't bode well for certain relationship developments IMO.