Wind Spell by Mallory Loehr

Joe, Polly, and Sam find three feathers and a message from the sky right before their camping trip.  They soon meet Athena from Greek mythology and have to go on a quest to help a lonely hero.

Joe is back and worse than ever.  I was almost hoping that he'd be gone for good after the last book.  His defining character traits are not believing in magic, being bossy, and being too good for his younger siblings.  He also believes his memories are dreams.  One has to be pretty far up the Nile without a paddle for that to work.

One good thing that's a constant between these books is that the kids know who the Greek gods are from reading schoolbooks, comic books, and other literature.  Many books featuring Greek mythology assume that the protagonists need to be told who people like Athena and Zeus are, even though a general grasp of the Greek gods is common knowledge, at least in America.

There seem to be no real similarities between the books in this series aside from the characters.  None of the adventures have any relevance on each other, and these three books don't really build up for anything in the fourth book.  The last book will probably be just another unrelated adventure.