@Melkor based on the fact that Josh Newman was mentioned I'm going to say it's based on a series the secrets of the immortal Nicholas Flamel. Reasonably good series, basically the gods as we know them were banished from earth for treating humans as cattle (which considering Prometheus literally created the human race is a bit of a turn). The magic system is based around auras each having a distinct smell as well as colour. Pure coloured auras are rare, pure Gold and Silver rarer and it follows a set of twins with a Gold and a Silver aura between them assisted by Nicholas Flamel and Perenelle to fulfil a prophecy and master the four elements. It's a decent enough book series but the thing that always irked me a little bit. The book spells it Nicholas Flamel but the real life man was French and his name was spelled Nicolas Flamel.

The immortals through the book got their longevity either through deals with the same gods that humans banished or in the case of the Alchemyst and his wife they sometimes find their own method of immortality. The former having the drawback of your patron deity being able to take the immortality away (unless you kill them but the cases where that applies are fewer and farther between than people who are able to make themselves live forever). There's also a species that existed before the gods, I vaguely recall them being called the Archons but they're a sort of sub plot that doesn't really go anywhere particularly interesting other than the implication of the gods being created...there's also this whole vampire thing. It's six books, there's a lot of material to work with but I'd be cautious about joining this roleplay, not least of which being Nicholas Flamel didn't discover immortality through alchemy, the book gave him the recipe and the recipe changes every time he and Perenelle use it so his son finding the recipe for himself breaks canon straight out the gate. I can see him making a deal and breaking it with a patron deity after getting his hands on the book (I forget what they're called in universe) but also wonder if it wouldn't be better for the book to end up in the hands of a distant descendent and starting the journey from there...I have interest in the universe, cautious about the concept as presented.