This is one of the key questions and a possible catalyst for Jeremy's nascent hatred towards his mother,which really started the whole thing..
possibly

like I have said before I look at it from both sides. But the stronger disparity appeared to be between Sheila and her mother .
Perhaps Jeremy was more adept at hiding it ? He too seems to have a split personality with similar accounts of him being popular and friendly and then being an odd ball.
so far I am surprised about how ill June had been and how the family tried to keep everything private . Jeremy was right about that . They did seem to want to try and cope with everything themselves and considering both Junes and Nevilles background, their problems must have come as quite a shock - they do seem to be of the generation that just shut up and got on with things.