You cannot have simultaneous database access through Dropbox. Short of using Sync as intended and requiring your friends to be running DEVONthink on each computre, the closest thing would be the Web Sharing UI. You will need port forwarding if the machines are not on the same network. This is NOT something we do but you can check out something like Lighthouse to do this.
So what you’re saying is that we’d have to have a sort of signal that one of us was using the database, and then when we’re done with it, we close it down and then a second person can open it up and start using it?
I.e. we could sync over dropdav that way, but we’d have to make sure that only one person was using it at any one time.
DEVONthink does not support multiple simultaneous users of the same database instance. You could make two copies of a database, and the three of you could work with those three separate instances. You then synchronize those three instances with a single syncstore.
Jim mentioned the alternative – web sharing (DEVONthink Pro Office only)