So the team line-up looks like this -
Lecher Onee-chan + Airhead Imouto
Tsundere Onee-chan + Pervert Loli Imouto + Shy Super-loli Imouto
Yep, this looks like a recipe for crazy.
Maybe it's my inner weeb talking but those untranslated "hentai" and "imouto" (among other things) make this manga a lot funnier to read. Those actually made me chuckle.