I like those, I like the Cassie one best, it would be so her to turn into an animal and then just move in with them for a little while! She'd write the best nature books too, no one else could write a book from the animals POV and know exactly what they were talking about.
It's a bit depressing and also Poe-esque, but I quite like the idea of Jake going a bit mad because of all the responsibilities and moral judgements he had to deal with at such a young age. As in, the war is over and all he knows how to do is command, and now he can't do that anymore he feels like he serves no purpose and perhaps succumbs to depression, substance abuse, things like that. That, or he was holding it all in for the good of the earth and then just fell apart as soon as it was over.
But then again that's a bit of a slur against a character who proved himself to be strong regularly throughout the series, so I've mixed feelings about it.
Although, I could not change Rachel's death. I do like dark plotlines, and Jake having to send his cousin to kill his own brother is just so dark and twisted that I wouldn't change it. It was the most moving scene in the whole series for me, I actually got teary!