Norman's Heritage

Most of what is known regarding the history of the Osborn family is revealed in the Revenge of the Green Goblin mini series.  During that story, Norman states that his great grandfather, Alton Osborn, was responsible for building the Osborn family fortune.  Alton was what is known as a robber baron, a businessperson that amasses large amounts of wealth typically by means of unfair business practices.  Any specifics on how he accrued the wealth are unknown at this point.  Unfortunately the wealth did not last forever. 
In Spectacular Spider-Man Annual #14, it is revealed that Amberson Osborn (Alton's grandson and Norman's father) lost the family fortune.  Amberson claims to have been cheated and that someone had stolen his invention.  Whether or not his claims have any validity or what specifically this invention was, are both unknown.  This information is told through Harry Osborn's recollections of the family history and Harry states directly "[that] the memories...may not be totally accurate but they are true!" 

Norman's heritage gets a little more confusing though, in Peter Parker Spider-Man V2 #25 Norman states that his father's name was 'Norman Osborn the first'.    I'm not quite sure as to how/why the name was changed, or what Norman's father's name is supposed to be.  It could be possible that the mixup came from a source of information similar to that found in the Official Handbook of the Marvel Universe Book of the Dead V9 shown below.  In that handbook it lists the various Goblins using Roman numerals before each name.  The entry, shown below, can be read as if Norman's full name is Norman Osborn II, implying his dad is Norman Osborn I.  

It should be mentioned that, technically speaking, Norman's father's name could have been Norman Amberson Osborn, if one wants to assume that Norman is 'the second'.  However, in Ms. Marvel (V2) #34 it is confirmed that Norman's middle name is Virgil, in that case he cannot be a 'second' because he does not have the identical name of his father.  An additional clue that Norman cannot be 'Norman Osborn II' is found in Peter Parker Spider-Man #89 which occurred during the Spider-Hunt saga.  The take home point here is that Norman cannot be 'the second' because his grandson is Norman 'Normie' Osborn the second.   

For simplicity sake, this site will use Amberson Osborn for Norman's father's name, since it was the first name that was published by Marvel. 

Alton Osborn as seen in Revenge of the Green Goblin #2

Amberson Osborn as seen in Spectacular Spider-Man Annual #14

News broadcast refers to Harry's son Normie as 'Norman Osborn the second', as seen in Peter Parker Spider-Man #89