To the first: well... each of the main characters could be said to embody an attribute that the Greeks considered heroic, and beauty would definitely be on that list. And to be fair, even Cronus has lampshaded this. To the second: hell, why does Jason have any descendants? Didn't his bloodline sort of end when Medea killed their sons?
In one episode the team goes to great lenths to design a trap for Cronus that consists partly of a one way portal directly to his cell in Tartarus. At the end of the Episode the plan falls apart but Cronus still falls into the portal and winds up in his old cell. Cronus is beat, series over. Except in the next episodes he's free again and he was never shown escaping from his cell a second time. What gives?