James is actually James Bond Sr's sonCome on! This is James Bond we're talking about. The "nephew" part is just a ridiculous lie probably to keep the boy safe (Not that it works very well)
James is the NEXT James BondA popular theory about the film franchise is that its use of The Other Darrin is in fact more of a The Nth Doctor; all those different looking Bonds are completely separate people, with the code name "James Bond" being passed down when one of them dies or retires. And here we have a kid using that name and training as a secret agent while still a teenager. Coincidence? He's actually being groomed as the next replacement Bond.
Goldfinger is Goldfinger's twin brotherThe original script for Diamonds Are Forever had Goldfinger's twin brother out for revenge. This can explain why he is still alive. He's not. It's his brother.