If you guys don't mind sharing your entire OmniFocus databases, you can use our existing synchronization stuff without going through multiple iCal. If your Macs and iPhones are all using the same sync server settings, the data will be synchronized across all the devices.
What you'll be lacking is the ability to add an action that you see on your machine/phone but not on your assistant's; the sync was designed around a one-user workflow, though this may change in some future version of OmniFocus.
That help at all?