what were pip's first impressions of his parents, and where had he derived these from?

Pip's first and only real impression of his parents is formed from his observations of their gravestomes. Pip tells us in Chapter 1 of the novel

'The shape of the letters on my father's [tombstone] gave me an odd idea that he was a square, stout, dark man, with curly black hair.'

Pip also makes similar deductions from the inscription on his mother's tombstone thathis mother 'was freckled and sickly.'