I think i got an answer for the Jevin
Jevin was in either someway trying to prevent this by not telling them, and even if he did im pretty sure characters like Raddy or even Clukr and Garnold would not be convinced and most likely The Sprunkis would side with Raddy over Jevin. he would try to convince them until it was too late.
If you analyze how he looks, it doesn't look like he likes to talk to the others or the others thinks that he's insane, his mood is entirely different also which can really help us understand how he feels, he knows it all and expects worse.
BUT THATS JUST A THEORY!! A GAME THEORY!! THANKS FOR READING!