1) Both editors start with an identical set of media assets
2) If possible, those media assets should really be all lumped together in one folder.
If this is the case….the Premiere Project file can be sent back and forth without the media and can be relinked on either machine.
If an editor creates additional media (like Photoshop files for example) they need to be passed along as well so that the media assets at both locations stay in sync.
you might look at https://www.dropbox.com as a way to create a collaborative portal between the two locations.