We have 3 main CADers (myself included), we essentially split up the work. All three of us know each other well enough, that we know how each other think, so working together and making a part to fit into a bigger design is easy.
The main idea formation process is just whoever comes up with the idea. For example, while we were working on the shooter this year, the main overview idea was made by a parent (we are a small team only 8 students and 3 mentors), than the parent built a prototype out of wood, and showed it to one of the CADers. It was up to the CADer to create that basic design in CAD, but it was also up to him to figure out how to make everything work (of course, getting advice every step of the way). Everything else was essentially done the same way.
Speaking about workflow, again we 3 just split up the work. This year, one person started on the shooter, than we came up for the idea for the drivetrain, so I started on the drivetrain, than we came up with the idea for the intake, so the third guy started on the intake. We just kept cycling like this.
Now once each various piece was created (for example when the shooter was created), than the file was handed off to me, to incorporate it into the main bot. It was easier this way, because one person would have the main overview, and know what needs to be done, without any confusion created by miscommunication.
So for your team, I suggest you have one “lead” CADer, who maintains the main project, while everyone else works on individual parts. And most importantly, make sure all three members on the CAD team get along, it will be real hard to get work done, if there is continuous argument of how something should be done.
Let me know if you have any other questions or need advice/help! Good luck with your CADing!