There is an interesting book called Jesus for the Non Religious which details the fiction in the new testament.

It is written by a retired bishop who is a believing Christian theologian interested in getting at the truth behind the bible. An amazing percentage of stuff that most christians take as gospel seems to be patent fiction when it is analysed.

Its a while since I read it but apparently Joseph is almost certainly an invention and Mary was most likely an unlucky lower class woman who was put up the duff by some cheeky wideboy.