[policarpo]

A few things to add:

You could just buy 1 license and set up separate logs in into OSX for each of you. This would allow you to keep separate databases if you can install OF just to a specific user.

Then you could each log into the free OG Beta Server to access your tasks on the iPhone.

How many Macs do you have? I think you can install OF on up to two machines provided they aren't running at the same time on the same network.