John Dashwood doesn't seem to regard (the second) Mrs Dashwood as a mother-figure, or expresses any warmth or filial concern for her... that makes me wonder about his childhood, and what age he was when his mother died, and where he went after that and who raised him. If he were 8 or 10 I suppose he could have been sent to school... but if he were younger?

With Mrs Dashwood's naturally warm and generous nature, it's hard to imagine her being un-motherly to a stepson in her home. Maybe John was being raised elsewhere.

John and Elinor and Marianne don't seem to have the shared history or the sense of intimacy that siblings raised in the same house by the same parents would have (even with a large age gap).