315 to 326 are NTR - the guy with brown hair is MC's older brother, who can swoop in and claim one of the girls if you don't praise her efforts to please you. (The girls would prefer you as their master, but they'll accept him if you brush them off. It's been a while, but I remember the older brother being a huge asshole who views the girls as barely better than animals.)
Reconciling with the girl the big brother's trying to claim results in 3 way make-up sex, because the MC is a lucky bastard.