If you have one person working on mapping and another on eventing, let the person doing the mapping create the maps. The person doing the eventing would need to copy the Mapxxx.rvdata2 file (for each map) as well as the mapinfos.rvdata2 file into their own project. Then they could work on eventing. While it's okay for others to LOOK at the map, nobody else should make changes to it while the eventer is working, otherwise you'll get two versions of it, both with valid changes.
So you don't have to finish mapping on ALL the maps before the eventer gets to work. You can do one map and pass it on to the eventer, then get to work on mapping the next map.
Just have one person in charge of adding new maps in the editor - their mapinfos file will be the one that everyone else will need to copy.
If you are all sharing a repository, like ALL working on the same project on dropbox or something, you should be even more strict with this - if anybody changes the wrong thing and saves, that's going to give EVERYONE an incorrect version. And whenever you save your project, ALL the database files (Actors, Enemies, Items, Skills, States, etc) are replaced, even if you didn't touch any of them. I'd much prefer to have a central repository that's only updated when you choose to, and only with the files you specify, and for anyone working on the project to have their own copy separate to the central one.
Edit: in response to your last post (which wasn't there when I started)
YOU insert the maps into the project and name them. Then save your project and give the others the files. Then allocate which maps they will each work on. They can each work on 3 different maps and give them back to you when done, and you can just copy them back into your project. The reason YOU have to insert and name the maps, then give them the mapinfos and the Mapxxx files is so they all have the same list of maps with names and parent/child relationships, and so you won't have two people working on Map001 thinking they're different things.