(And I doubt Lyle will win because there is no one source to lay a lawsuit on, all the gem dragons are likely to deny they owe anything anyway, he doesn't actually have a court to take the matter to, and so on. If he actually separated out all the ones that took money, got them to admit taking the money, got them to admit that they should show up at court over it, got them to actually show up at court about it, and had a court for them to show up at, maybe, but as is I doubt he'll get anything from even one dragon. No group suits for the dragons when they're all independent and you'll have to go after each of them individually.)
(And of course, his first issue will be proving that they are actually one of the dragons that took money, instead of one of the ones that didn't hear about it in time/was busy with something else/was too far away at the time/was otherwise distracted. And you know none of them are going to admit anything to someone who wants to take away their shinies.)
(Also, beyond that remember that each constellation only effects the word they are actually on, not both worlds. Which was it that had the war going on again? Because the Staff is only on World A.)
(As for the rest of the stuff, he doesn't need to take any dragons to court. You're thinking too modern. This is a land where gods, dragons, monsters, and magic all live under the same metaphorical roof so it would be unwise to think that the world functions exactly the same as our own - in this case in regards to law.
Here's one way I think could happen: Lyle goes to the High Temple. He tells them they have to pay back the Empire for the money the Gem Dragons stole as the highest representatives of the race. When they inevitably decline, he mentions that they're the High Temple of Greed not the High Temple of Gem Dragons and goes on to say that if they would be going against the will of Azem by actively attempting to stop the pursuit of the greed of other races. If - as is most likely - the High Temple says that if they do pay they'll be stopping the pursuit of greed of Gem Dragons at which point Lyle will cut them off and sue them for being racist by accusing them of disregarding all other races to put their own at an advantage. From there they have to either pay a large sum of money, or pay a large sum of money AND be seen by everyone as a bunch of racist gits.
I'm just going to say now that the arguments in that example aren't all that great and they aren't airtight but IRL I'm just a mere human - I am physically incapable of coming up with the arguments capable of the First Lawyer that has blessings from both the god of humans/ambition and the god of LAW, as well as being under a powered constellation that gives a bonus to law. Besides that, international/Gem Dragon law hasn't really been touched on so Lyle can make shit up as he goes and it'll all be canonised.)
Hahahaha. No. What will happen is that the High Temple will laugh in his face, point out that they are not the highest authority for the gem dragons/never took any money in that incident, flatly refuse to pay up anything, and then kick Lyle out. As you said, High Temple of Greed, not of Gem Dragons. They aren't responsible for humanity being foolish enough to pay Gem Dragons a lot of cash and not get anything out of it.
IE, The High Temple of Greed isn't the highest representative of the Gem Dragons, it's the highest Representative of the god of greed and his followers. Not the same thing. Other people, and especially other gods, being foolish and lax with their cash isn't their problem /at all/.
Any Lawsuit that tries to get the Gem Dragons to pay up by going through them is about as likely to work as any other Lawsuit that tries to get People A to pay up by Lawsuiting People B. In other words, it's not going to work at all.
Edit : You accused me of 'thinking too modernish' about this, but bluntly, expecting a lawsuit to work at all, or even be relevant, is your 'thinking too modernish' problem.
EditEdit : also, as a reminder, the Staff is the Constellation of Law, not Justice, so it'd help whoever you are utterly failing to sue just as much.
Well, I'm having some RL problems, can I get put in stasis for now?
Good luck with whatever the issue is.