Ubuntu :: Share A Folder With R/w Access By Two Local Users?

This seems like somewhat of a n00b question, but I'm kind of stumped and working on a half a dozen other things at the moment, so I thought I'd go ahead and ask it.

Is there a "correct" way to set up a shared folder between two local users using only EXT4 that will allow both users read & write access to everything in the folder?

Here's my scenario: My wife and I use the same computer. I want two separate user accounts (mine and hers), but I want ~/Music to point to the same location for both users so that I don't have to duplicate all of the files.

Too protect the innocent, I'll use Jack and Jill.

So say Jack downloads or rips an album:

"/home/jack/Music/Radiohead/Ok Computer"

I want Jill to be able to able to create a folder:

"/home/jill/Music/Radiohead/Hail To The Theif"

I know the basics of symlinks so I can get /home/jack/Music and /home/jill/Music to point to the same place. I also have Jack & Jill in the same group.

The problem I'm having with my test setup is when Jack creates "/home/jack/Radiohead", it is set up to where Jill can read, but not write. So she can play songs from Ok Computer, but if she wants to download Kid A, she has to go in and manually change the permissions on Radiohead first.

Also, while I might set up multiple directories this way, what I DON'T want is for Jack to be able to modify /home/jill/otherdir where otherdir is just a regular directory set up with default permissions.

Oh, and as an added bonus, it would be nice to set up another account (i.e. a "guest") with limited permissions that can read, but not write/modify.