Since Cyseal is clearly in a vastly different geographic location than Aleroth, and there's no reason why those bodies would be moved across the country to a tiny town's tiny graveyard and stay there for 1200 years, I am going to assume that these are all different people with the same names. That's the simplest explanation.
It's obviously a different Thelyron, since Mardaneus met one who was alive, Thelyron was a healer in the village. Thelyron's (helpfully dated) journal entries you can find in the catacombs indicate that he would only need to be dead and wait in the afterlife for 11 years before his machine could revive him.
