Responses
I got lost when h kept saying “nee-san” is coming. Whose nee-san? The two brothers’ or kazumi’s? And where is kazume’s mom?
He
nee-san is Reiko, Kazuomi's mother and Masaki(nii-san)'s wife
If it's a "nee-san" it's a "she" therefore, Shinobu is referring to the wife, Reiko. If it is a "nii-san", then what Shinobu was referring to a "he" therefore his brother.
Coulda shown the little sister and mom (more than a panel). There's no good reason as to why women are so often faceless in yaoi, particularly the ones in which women aren't evil mothers/exes.