Pretty sure the "grandson" is supposed to be his granddaughter. She's called Miko, and has clear breasts on pages 6-7. She's just a bit plain and not very feminine, which is why the producer pushed her to dye her hair.
Not sure if Shima and his colleague not recognizing that is intentional, or you've just had to assume it was a man in the TL since it is never clearly brought up.