When it comes to the Father, his entire family (parents and brother) died when he was 10. It's entirely possible that before he was adopted by his Wife's family, he went through the care system which can be traumatic (loss of support systems, constantly being moved around to different systems, unable to connect and form attachments due to the transitory nature of the adults present).
It can be quite common to lose memories from periods of intense grief and tramua. It's a coping mechanism. But his experience means that he knows how Kuromi would be reacting and whether she's truly expressing herself.