One's flesh and blood may refer to one's family, or may denote all mankind. It is also used to denote the living material of which people are composed.
The earliest usage of this phrase relates to the general 'mankind' usage. This comes from an Old English translation of the Bible - the Ags. Gospel, Matthew XVI 17, circa 1000: "Hit ye ne onwreah flaesc ne blod."
The later King James version lists this passage as:
And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven.