Josh,
You really need a dedicated shared storage and project environment to make your job work efficiently in the manner you describe with at least two clients. Project sharing and media sharing at a sustained and manageable rate is not trivial and hence why these systems cost considerably more than the Drobo.
May I draw your attention to the following post https://forums.creativecow.net/readpost/305/260 where an EditShare system called a Field 2 is described which would fulfill your requirements. Not only does it support shared storage of media, but also project sharing for Premiere Pro as well as media management.
Feel free to contact me, kevano@editshare.com , and I can arrange a web demo of the EditShare environment working with Premiere Pro and address any further questions you may have.
Kevan O’Brien
Senior Workflow Specialist
EditShare